Thanks for the info Allan L and nicanary. I trusted some internet sources that were clearly not up to scratch. It now seems clear that this was Peugeot's first 4-cylinder, but not first propietary engine.
Yes the internet is full of traps for the unwary!
So are some books, of course, and they can't be changed but internet items can be, if the originator can be found and contacted - and Wikipedia can be edited directly, although there can then be a edit/re-edit battle.
Keep up the good work Monty!
ETA: Peugeot Type Numbers were not used at the time but appeared when someone compiled a book about their cars in more recent times.