I was under the impression that Roman traders and merchants often went where Roman legionaries never trod.
I was also under the impression that Roman coins were often legal tender in places even the Romans barely knew existed.
I think you are correct. Who is to say that it wasn’t brought into Wales by someone who lost it traveling around Britain in any ensuing time between then and now!
Correct. Not because they were Roman, but because in ancient times no one cared who minted the coin; only its metal content and weight. If a certain mint's coinage was more preferred in some parts, it was because of the mint's reputation for metal purity and consistent weights.
This remained true up into the 19th century. The USA used foreign coins as legal tender for many years: the Spanish 8 Real (frequently cut into pie shaped wedges for change, hence: “2bits; 4bits; 6bits; a dollar” and “pieces of eight”) and the highly reputable German/Austrian Thaler, which is pronounced “Taller”, eventually becoming “Dollar.”