In the trail-off of a Capitol record from the 60's - 70's, you are likely to find something like this:
ST - 1 - 2553 - B8
The first component is the prefix. "S" (after 1958) denotes stereo. "T" is the price code (price codes "W", "M", and later "O" were also used on Beatles records.) If the record had inserts or a fold-open cover, two more letters were added. The third letter is the total number of records in the set (A=1, B=2, etc.) The fourth letter is the type of packaging.
The second component is the side. (1, 2, 3, 4).
The third component is the catalog number.
The fourth component tells what set of stampers were used, as follows.
From the 50's D was used to denote 1st press mono records. When a second dub of the master was made, N was used. In the 60's, F and G denote 1st issue mono records. P and T denote 2nd presses.
For stereo records, A and B were used the first issue. W and X were usually used the second time, but sometimes H and J were used, as on the White Album. [This may have been the case because the White Album's problem was actually the banding and not the sub-master.]
In 1969, after stereo took over completely, Z began to be used for some first pressing (stereo) records. This letter became the convention of the 70's, occurring on most Apple issues.
The number after the letter may have something to do with the actual stampers. So, B8 might denote the 8th stamper made from the first sub- master. NOTE: the Winchester factory never started with A or B when reissuing Beatles records. It is thought that they received their copies of everything from Scranton.
info. quoted from http://www.eskimo.com/~bpentium/capitol.html