Maybe that's it. I have seen a few pre-1960 Petersons with a Swedish hallmark (no date), below the 'no date' hallmarks Peterson was using during that period.HALLMARKING CONVENTION
Hallmarking Convention is an international treaty between States on the cross border trade in precious metal articles illustrated in The What is? Silver Dictionary of www.silvercollection.itwww.silvercollection.it
I have/had a couple of Pete’s (late 80s/early 90s) with these marks and I assumed they were just for sale in Europe.