I am trying to figure out approximate dates for some old photo prints. A lot of them have codes printed in one of the front corners (e.g. "Jan M491", "Jun M391", "Aug M488", etc.)
The first 3 characters obviously seem to be the month they were printed, but I am not sure about the last 4 characters. The last 2 could represent the year, but they could be totally unrelated. The above examples appear on prints that definitely were from somewhere around the 1991 and 1988 timeframes, but that could just be a coincidence and I'd like to be sure.
The codes are not unique. There are batches of photos that definitely came from the same roll and have the same code on the print.
Attached is an example of the code in the top right corner of a print. The second example with Jun M289 is 100% from Jun 1989, since that graduation took place in May 1989. This makes me strongly think the last 2 digits are the year, but it would be great if someone could confirm those codes work that way.
I've searched many sites related to dating old photos, but I haven't found any mention of that type of code.
Does anyone know how to interpret those codes?