My *guess* btw as to the MPxxxx markings with the MSl△xyyzz style datecodes (with 5 digits; the old ones use 4 digit YYWW year + week datecodes) is:
MS - ?
l = location of manufacture?
x = last digit of year (first digits are 198)
yy = week during year
zz = day during week (first digit is always 0)


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