I thought it might be helpful to write a short post on matrix numbers to help users of this site.
A matrix number is intended for the internal use of the record manufacturing plant to manage and track the pressing of recordings, but are also studied and documented by record collectors, as they can sometimes provide useful information about the issue sequence of the record.
There are two parts of the matrix number to be considered:
-the main number, (which is usually inscribed on the surface of the recording (and sometimes printed on the label as well), and
-extra information (which can include a cut or take or session number).
Matrix numbers can refer to any of these elements, or all of them combined. The inscription area may also contain record plant codes or logos, the initials or signature of the disc cutting engineer, as well as cutting and/or copyright dates, among other things. Often, the element of this number may indicate the sequence of a recording in a series of recordings.
‘In the days of 78 rpm records, before recording tape was commonly used, audio recordings were cut directly to disc. The recording studio would assign a number to the recording, which would become the main part of the matrix number, and often several takes would be made. In most cases, only one take would be selected for issue, but there are occasions where alternate takes were issued as well – especially if the original master was damaged or beyond further pressing use.’  This additional number is often refer to as take number.
Alternate takes are of interest to collectors, particularly if it is jazz or dance band music. Since jazz and dance band music was often partially improvised, alternative takes could contain significant differences, and a comparison of two or more takes can reveal which portions of the music were pre-determined, and which were improvised or variable. Also, when more than one take was released, one is usually much more common than the other, and the less common take or takes can become a valuable record to collectors.
In most cases, collectors can easily determine the matrix number of a 78rpm. As stated earlier, the matrix number is most always inscribed or pressed into a disc’s surface, (and is usually found in or between the runout grooves and label). In many cases (but not all), the matrix number is found at or near the 6 o’clock position relative to the label’s correct readable orientation.
In most cases, the matrix number is comprised of two numbers – the source or session number and the take number. In the above illustration, the main session number is recorded as 2B 6715 and the take or session number (issued), is III (or the 3rd session).
- Edited text from: https://en.wikipedia.org/wiki/Matrix_number
This following sites may also be of help. [All links open new windows]