"Peugeots built in France during the 1980's can be dated by year through use of their serial numbers. Following a letter prefix, typically Y or B, the first number of the numeral code indicates the bicycle's model year (ex. PKN-10 #B 0667631, built in 1980). Track bicycles, at least, appeared to have their numbers stamped on the left rear dropout."
Source= think's link above.
I'm not sure when they started putting the numbers on the sticker. I've two bikes I've pretty well dated to 1973, with the serial#s on a plate, and one from 76, two more from 79/80, another from 84, all stickered. The PH designation places your bike solidly in the eighties, though. Don't think it was used prior to that.
Check your bottom bracket; if it's English thread, it's definitely 80s. If it's French,
70s or before. Swiss, late seventies early 80's. Swiss is the same as French, only reverse threaded on the fixed cup.
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