French releases can be a nightmare when it comes to date the releases, so I thought it is time to bring this up to a broader public. Here some useful hints on how to (roughly) "date" a French release (or at least to exclude a date):

The French price code system consisted of 5 phases:

Phase 1 (until 1946):
The colour of the centre labels, in combination with the size, was the price indicator.
However, every record label had it's own colour system.

Columbia:
25 cm, black: 18 FF
25 cm, brown: 21 FF
25 cm, red: 22,50 FF
25 cm, blue: 25 FF
25 cm, violet: 36 FF
30 cm, black: 25 FF
30 cm, brown: 35 FF
30 cm, red: 37 FF
30 cm, blue: 40 FF
30 cm, violet: 48 FF

Disque Gramophone:
25 cm, green: 18 FF
25 cm, black: 25 FF
25 cm, red: 37 FF
25 cm, cream: 45 FF
25 cm, violet (after 1929): ?
30 cm, green: 25 FF
30 cm, black: 40 FF
30 cm, red: 55 FF
30 cm, cream: 62 FF
30 cm, white: 95 FF

Odeon:
25 cm, blue: 18 FF
25 cm, green: 22,50 FF
25 cm, red: 25 FF
25 cm, mauve: 30 FF
25 cm, light brown: 25 FF
25 cm, white with black (reissues): ?
25 cm, white with blue (reissues): ?
25 cm, white with green (reissues): ?
30 cm, blue: 25 FF
30 cm, green: 32 FF
30 cm, red: 40 FF
30 cm, mauve: 45 FF

Parlophone
25 cm, black (after 1929): ?
25 cm, blue: 18 FF
25 cm, red: 18 FF
25 cm, brown: 22,50 FF
30 cm, blue: 25 FF
30 cm, red: 32 FF
30 cm, brown: 37 FF
30 cm, light blue: 40 FF

Pathé:
25 cm, black: 16 FF
25 cm, green: 18 FF
25 cm, red: 20 FF
25 cm, violet (after 1929): ?
25 cm, white (after 1929): ?
30 cm, red (after 1929): ?
30 cm, black (after 1929): ?
30 cm, green (after 1929): ?

Pathé Art:
30 cm, multicolour, blue border: 35 FF (1929)
30 cm, multicolour, orange border: 35 FF (1929)

Polydor:
25 cm, green: 18 FF
25 cm, blue: 24 FF
25 cm, black: 24 FF
25 cm, violet: 24 FF
25 cm, red: 34 FF
25 cm, white with green (reissues): ?
30 cm, green: 25 FF
30 cm, blue: 40 FF
30 cm, black: 40 FF
30 cm, violet: 40 FF
30 cm, white with green (reissues): ?

Note: NP in a circle indicates the shellac was made of "recycled material". It was introduced 1939, shortly before WW II.
The recycled material allowed a much cheaper production but was very fragile and had far more surface noise.

Phase 2 (1947 to 1968) - "code-prix conseillé":
All French record labels used a common, state-imposed system called "code-prix conseillé", which consisted of either the wording (Série Artistique / Série Standard / Série Médium), or a single letter, usually encircled and found on the back cover and the labels:
Ⓐ or A = Artistique (the most expensive price, usually for classic and high volume artists).
Ⓜ or M = Médium (medium price. Basically for the majority of releases).
Ⓢ or S = Standard (cheapest price, normally for "dance music" or reissues)

Later the record companies added their own letters, e.g. Philips = D for Deluxe (introduced 1959 for classic records with a lower price than A), or P for Populaire (introduced for records cheaper than S). Example: An LP that would have cost 25 Francs before would then go out for 9,95 Francs only.

Pathé Marconi used an alternate price code system (between 1967 and 1968 only):
A: Large orchestrations
B: small or medium orchestrations
C: Solo artists
D: Foreign artists.

Phase 3 (between 1968 and 1978) - "lettres-codes":
Introduced by the "Syndicat national de l'édition phonographique" (SNEP), consisting of 1 letter (later 2 letters). Usually found encircled on the back cover, top right hand side. The code corresponded to a common price, imposed on all record companies and (due to state-imposed fixed margins) on retailers. So, the retail price resulted automatically.

For LPs there were now the following codes:
A, D, M, S
T, U - introduced 1968
B, C, E, F, G, H, R - introduced 1970
I, K, Q, W, X - introduced 1971 (Q and W were used for import records)
Z - introduced 1972

Prices were fixed by the Ministry of Finance until 1972. After that, the record companies had more flexibility in their price policies and hence more codes were introduced, until the whole alphabet was in use:
O - introduced 1973
Y - introduced 1974
FB - introduced 1975
V, KC, RB, SE, SF - introduced 1977

Double LPs had:
2xF (ca. 17 FRF), 2xD (ca. 21 FRF), 2xT (ca. 25 FRF), 2xC (ca. 30 FRF), 2xU (ca. 35 FRF), 2xS, a.m.m.

Attention in case of reissues: when the price for the record didn't change, the price code didn't either. So you may very well find a price code from 1969 (T) on a Pink Floyd album of 1975. It's also possible that there are several reissues with different price codes. Because printing a new cover for each price change was too expensive, the companies simply used small stickers, covering the old price codes.
See here for an example.

Generally, you can group the various LP price codes (26 altogther in 1978) in three categories:
Budget-line (for established releases, between 10 and 25 FRF in 1978): codes D, E, F, G, H, R, V, Z, FB, RB.
Medium price (between 25 and 35 FRF in 1978): codes B, U, C, T.
New releases (between 35 and 50 FRF in 1978): codes A, K, O, S, X, Y, SE, SF.
Special releases (higher than 50 FRF in 1978), codes I, Q, W, KC.

There were 2 major price adjustments in 1974 and 1977, leading to higher prices for all price codes.
A: 37 FRF (1970), 37,50 (1972), 39 FRF (1974), 40 FRF (1977)
B: 32 FRF (1970), 34 FRF (1974), 34,50 (1977)
C: 26 FRF (1970), 28 FRF (1974), 28,50 FRF (1977)
D: 20,50 (1970), 22 FRF (1974), 22,50 FRF (1977)
E: 10 FRF (1970), 11 FRF (1974), 11,50 FRF (1977)
F: 16,50 FRF (1970), 17 FRF (1974), 18,50 FRF (1977)
G: 16 FRF (1970), 16,50 FRF (1974), 17,50 FRF (1977)
H: 11,50 FRF (1970), 12,50 FRF (1973), 13,50 FRF (1974), 13,70 FRF (1977)
I: 60 FRF (1971), 64 FRF (1974), 65 FRF (1977)
K: 32,50 FRF (1971), 45,50 FRF (1972), 48,50 FRF (1974), 49,50 FRF (1977)
O: 45 FRF (1972), 47 FRF (1974), 47,50 FRF (1977)
Q: 57 FRF (1971), 60 FRF (1974), 61 FRF (1977)
R: 13 FRF (1970), 13,50 FRF (1973), 14,50 FRF (1974), 14,90 FRF (1977)
S: 38,50 (1970), 40,50 FRF (1974), 41,50 FRF (1977)
T: 24,25 (1970), 26,25 FRF (1974), 26,50 FRF (1977)
U: 28 FRF (1970), 30 FRF (1974), 30,50 FRF (1977)
V: 14,50 FRF (1977)
W: 49,50 FRF (1971), 52,50 FRF (1974), 53,50 FRF (1977)
X: 40,50 FRF (1971), 48,50 FRF (1974), 49,50 FRF (1977)
Y: 36,50 FRF (1974), 37,50 FRF (1977)
Z: 20 FRF (1972), 21 FRF (1974), 21,50 FRF (1977)
KC: 52 FRF (1977)
SE: 46 FRF (1977)
SF: 46,50 FRF (1977)
FB: 19,90 FRF (1975), 19,95 (1977)
RB: 16,50 FRF (1977)

For 45rpm singles the codes were:
L (since 1968) - 8,50 FRF (1978)
J (since 1972) - 9 FRF (1978)
M (for EPs - since 1968) - 12 FRF (1978)
N (since 1974) - 9,95 FRF (1978)
E (since 1975) - 11,50 FRF (1978)
EA (since 1978).

Company specific 7" codes:
NA (since 1972)
LA (since 1974) - 8 FRF (1978)
PN (since 1974) - 6,10 FRF (1978)
R (Barclay und sublabels only, since 1971) - 14,50 FRF (1978).
EC (since 1977)

Usually, the price codes changed in the last quarter of the year, therefore the overlaps in years. E.g. the code valid for 1973 (B) was in fact introduced already around October 1972.

Phase 4 (1979 until late 1984):
Company specific price codes: PM, POL, AE, PG, BA, CB, etc. (see list below for abbreviations).
The price code coming from the record company was not binding for the retailers anymore, they now could freely add their margins on top.
Please note: Even though the general boundary is 1979, it is possible that a new price code was already present on December 1978 releases, in conjunction with the old price code.

List of known French company price code letters
AD = Auvidis
ADE = Adès
AE = Arabella Eurodisc
ARC = Arcade France S.à.r.l.
BA = Barclay
BAL = La Baleine
BM = BMG
BPE = Baillemont Productions Distribution
CA = Carrere
CB = CBS / Sony Music
CM = Le Chant Du Monde
D = Danceteria
DIS = Disc'Az
DK = Mélodie
FOO = Madrigal
HM = Harmonia Mundi
IM = Impact (2)
LA = Laurence Records
M7 = Média 7
MD = Moradisc
MU = Musidisc
NR = New Rose
OMD = OMD (3)
PG = Phonogram
PM = Pathé Marconi EMI
POL = Polydor
PY = PolyGram
RC = RCA / BMG
SA = Safari Ambiance
SC = Socadisc
SD = Sonodisc
UN = Universal
VG = Vogue
WAG = Wagram Music
WE = WEA or WEA Filipacchi Music
WM = WMD

Phase 5 (since August 1984):
Introduction of Barcodes.
French cassettes featured barcodes only since October 1984.

So, despite barcodes, record companies were still obliged to show Price Codes on the releases issued in France (i.e. also for Europe-wide releases not specifically mentioning France) (Art. 1, Arrêté du 12 janvier 1995 fixant les mentions obligatoires devant figurer sur les phonogrammes (consolidated version 2017)).

DL (Dépôt Légal - "Legal Deposit") at Bibliothèque Nationale de France (BNF): Only the first edition is subject to the legal deposit, all reissues get subsumed into it. So this date can be very useful for first editions but fails for reissues.

==============================================================================
For dedicated Virgin France price codes, please refer to this Wiki.

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EDITS:
09.08.2016: Order of the thread changed (Price code elaboration first, Virgin France excursion last).
Date corrected: Phase 4 (POL, AE, PM) already started with the beginning of 1979, not late 1979 (source: "Etude sur l'evolution de la concentration et des prix dans l'industrie et le commerce du disque en France" - Commission of the European Community, June 1979 - in French only).
30.08.2016: Info on DL at BNF added.
28.10.2016: Added another price code (SA).
02.11.2016: Clarification on being price codes only.
08.11.2016: AD price code added.
14.11.2016: SC price code added.
19.04.2017: Virgin France moved to dedicated Wiki page.
21.04.2017: Overhaul of codes, addition of LA company code.
30.05.2017: BM code price added.
13.06.2017: Pathé Marconi 1967/68 price codes added
07.08.2017: UN and CM codes added
16.08.2017: Label colour coding added
29.08.2017: Clarification regarding use of Price Codes after introduction of barcodes by French law (1995). NP on labels.
12.09.2017: Broken link corrected.
13.08.2018: Note about possible "early adoption" of 1979 price codes on late 1978 releases added.
14.11.2018: BAL and BPE added
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