Well -

It all started with King Edward II. He was the one who conquered Wales. He obviously had an eye for the future, because he set up a scheme under which one county of Wales would transfer to England every century until there was no Wales left. This process travelled down the England/Wales border, moving the border westward, which is why there are so many Welsh placenames on the English side, in what is now Shropshire and Gloucestershire. So Bridgenorth certainly could have been originally a Welsh town called Pontygogledd (your translation is correct). However, it's a pretty generalised name, and I wouldn't rule out there being other North Bridges in Wales.

FWIW, at the start of the 20th Century, Monmouthshire was due to transfer into England, and at the start of the 21st, Glamorganshire. This would have put Cardiff into England. Understandably, the English didn't want it, and the process was dropped. However, Monmouthshire did cease to be a part of Wales in 1901, and was not formally re-incorporated into the Principality until after the 2nd World War. The Declaration of War in 1939 was made in the name of "England, Scotland, Wales, Northern Ireland, The Isle of Man, the Channel Islands and Monmouthshire". The peace treaty in 1945 left Monmouthshire out, so Monmouthshire is still technically at war with Germany.

Andrew