Even when they don't explicitly give the month in plain text, as many do not, you can decode the first few characters of the serial number to give as much precision as you can ever get.
The first two, most often alpha only, indicate the location, as in SG for Singapore (very common), CK for Cork, just as two possibilities, and so on. The first numeric after that is the last digit of the year of manufacture, which needs that you know the decade, for which there are only three possibilities so far: the 1980s, 1990s and this century, remembering that humans begin numeration from 1, not zero. The lifespan of the Performas was limited enough to need no further definition.
The following pair of numerics indicate the week of the year, as 'during the nth week'. The following alphanumerics, in base 34 (using all alphabetic and numeric characters but I and O, for obvious reasons of potential confusion), indicate the sequential ('serial') number proper (and sometimes subtype).
For example, SG234(03RD11) represents a Classic made in Singapore in the 34th week of 1992, or SG337(0XNC2J) a Performa 250 made in Singapore in the 37th week of 1993, whereas a Colour Classic's designation would end in G.
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