Parlophone started pressing LP's before they associated with Capitol, so their numbering schemes are not related.

Back then, "A", "B", "C", and "D" were codes used to indicate the series that the record was in. You'll find many Odeon-series Classical recordings with the prefix PMA. PMB's were Odeon series records, too, but these were 10" LP's. PMC's were popular records, comedy records, etc. -- anything that wasn't in the Odeon series (this included British artists). PMD's were ten-inch versions of the kinds of records in the "C" series.

The "M" in the middle represented a Long Play album. I do not know why they used "M". The later-used "A" simply denoted an entirely different series; the "A" does not mean "Apple".

For example: PMA 1024 is Conchita Supervia Sings Carmen
PMB 1002 was a Mozart serenade by the Haas London Baroque Ensemble. The record was a ten-incher.
PMC 1007 was "The Gambler" by the Philharmonia Orchestra -- yes, that passed for "pop".
PMD 1069 was "The Best of Sellers" by Peter Sellers. Yep, it's a ten-incher.

So, the Beatles' first album, Please Please Me, had the catalog number PMC-1202. It was a Parlophone 12" record in the series containing British artists.

"S" was used in the place of "M" for stereo albums, and this was placed at the end -- apparently so as not to be mistaken for a different speed record. Originally, the PCS series was numbered differently from the PMC series, since not all records had both mono and stereo counterparts. Some record companies in the US had similar numbering conventions.

PAS-10001 was Judas Jump's album, Scorch -- released in 1970.
PAS-10005 was by the Hollies.

When Parlophone wanted to indicate that a record was an export album made in England and sent to another country, they used an additional letter at the beginning: "P" for "Parlophone" or "C" for "Capitol."

CPCS-101 was a British export of the American album, Something New. PPCS-7067/8 was a British export of the UK White Album to countries where the Apple trademark was not yet licensed.

The only prefixing created specifically for the Beatles while they were together was CORE, used on John's "Live Peace in Toronto 1969" LP. It's numbered CORE-2001; there were no other LP's in the CORE series.

If another letter was used AFTER PMC or PCS, this usually indicates that the record was MADE by a Parlophone affiliate in another country. This gets complicated, because if, for example, a Sweden-series record was used in another country, they'd KEEP the prefix of PMCS.

"G" = Greece
"H" = Holland (the Netherlands), not used during the Beatle period
"J" = South Africa
"L" = (unknown)
"M" = New Zealand
"O" = Australia
"Q" = Italy
"S" = Sweden

Now, the British Parlophone albums also had tax codes, mother codes, and stamper codes in the vinyl -- but that's a different story.

Identifying Parlophone Labels

This is how to identify the original Parlophone labels in the UK from the later releases, which are all very similar.

1963 -- black/gold label

1963-4 -- black/yellow label with "the Parlophone Co." around the rim of the label and NO "Sold in UK" message on the label

1964-5 -- black/yellow label with "the Parlophone Co." around the rim of the label; has "Sold in UK" message on the label

1965-9 -- black/yellow label with "the Gramophone Co." around the rim of the label; has "Sold in UK" message on the label

1969 -- black/yellow label with "the Gramophone Co." around the rim of the label and NO "Sold in UK" message on the label

1969-73 -- black/silver label with "the Gramophone Co." around the rim of the label; one EMI box logo on label

1973-6 -- black/silver label with "the Gramophone Co." around the rim of the label; two EMI box logos on label

1976-80 -- black/silver label with "EMI" in the rim of the label

1980-on -- black/silver label with "all rights..." in the rim of the label

MONO black/yellow label reissues from 1982-85 have "MONO" on the labels; original copies do not read "MONO."

Information thanks to Frank Daniels, one of the authors of The Price Guide for the American Beatles Records, 6th Edition.