>pardon me for asking Yet Another Stoopid Question, Jo, but how did "quotation marks" become "inverted commas"??

Ah that would be the rule of sixes. When I was six it was a word that I was taught so therefore it was correct and had existed forever. When you were six you may have been lead to believe something else and therein lies the problem.

The short answer is "search me". I've googled and all the rather eminent sites (newspapers and academia) that use the term are .uk or .au sites, so it must be a regional variation.
You could always seek out:
Burt, Warren. "Drones 1994 #2 - Old Commas Inverted and Revisited", Xenharmonikôn vol. 16, autumn 1995, p. 99 & 103 (score).