One of the first steps when making CDs is to produce a "glass master". From that (using a few more steps) a "stamper" is created which is then used to press the actual CDs.
When looking at a CD you can often see text in a ring in the middle of the CD. This is the so called matrix which comes from the glass master. Apart from the matrix other text (like the IFPI mastering SID code) could possibly also come from the glass master. A bit of background information can be found on page 7 of the IFPI SID code implementation guide although I would also highly recommend watching some of the clips about glass masters on YouTube, which are highly informative.
One company making a lot of these glass masters is Cinram. For most of their glass masters they stored the production date in matrix.
This is good news, because it means that it could possibly be used to verify releases and see if the declared year of the release is right: it could never have been released before the glass master was made. It could, of course, be released later, as some masters are made once and then the stampers made from these are used for years.
An example can be seen in this release: the glass master was made in 1993 (so there is no mastering SID code on it, as that was only introduced in 1994), but the CDs themselves were moulded in 1994 or later in a machine which printed a SID code in the mould.
A typical matrix from glass masters made in Canada by Cinram look like this:
"#931127N CD-26496 MFG BY CINRAM"
A matrix similar to this one can be seen on the pictures of this release.
The interesting part are the two digits following the # character. These are, according to a forum post on Discogs, the year the glass master was made (the number is actually the full date, either in YYMMDD or YMMDD notation). So what I can do is look for these patterns in the Matrix / Runout fields for each release with a matrix like this, extract the two digits representing the year and compare that to the year the CD was supposedly released.
In the data there are 4342 releases that have "MFG BY CINRAM" in the matrix, plus something else that starts with "#". The "CINRAM USA" matrix numbers seem to follow a different pattern, so I ignored those. The releases that I looked at are distributed over the Discogs dataset as follows:
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| Distribution of release pressed by Cinram with a possible year in the matrix |
I then looked at for how many releases I could do a check between the possible year from the matrix and the release year. I could find 567 releases, distributed as follows:
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| Distribution of releases with a possible wrong year |
I verified a few of the possible errors and although there might be a few where the matrix might not have the release year embedded in it the vast majority indeed seems to be wrong. A few releases were said to be from 1985 and pressed by Cinram, even though the profile page for Cinram says they didn't start pressing CDs until 1987.
There are apparently other pressing plants that also embedded the year in the matrix and somewhere in the coming few months I will look into these as well.
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