Hi guys,
Thanks M for your advice regarding the crack - I think I'll try that to stop it travelling further, it would be a great shame for it to end up in more than one piece after all this time.
Well, I sent a perfectly friendly and polite attribution request to Dorothy & Katharine at The Sandwich Glass Museum and received just one rather curious reply saying, and I quote: ''i don't THINK so.. would you respond? Thank you.''
No idea where to go now....