I'll go out on a limb here and say that you MAY NOT have an early 1970's PX-10s, you might have a late 1970's PX-10s. The ***531*** decal was introduced by Schwinn in the early 70's (maybe 72 ?? not sure), but the ***531*** decal for European frames was not introduced (at least on Raleighs) until 1977 (I have 2 such bikes, one Carlton, one Raleigh, and a 1976 531-db Raleigh without said decal), and so I believe that your decal must have a gold band saying, "(TI) Reynolds Tube Co. Limited", which indicates a post-1976 decal. Raleigh was about as close to Reynolds as possible, as both companies were owned by TI from 1976 onwards.
So the answer is, probably, Peugeot may have stopped using french-language decals in the late 1970's, so you got the latest 531-db decal, but I wouldn't know why they abandoned french, OR, you have a replacement decal on your frameset, and the bike could be any year.
If your frame lacks a gold band at the bottom, then I'd say it's almost certain that it's a decal intended for a Schwinn Paramount which was diverted for use on a Peugeot PX-10s repaint.
- Don Gillies
San Diego, CA, uSA