thanks for all replies
1).......yes, you correct Sue, and they are also referred to as 'Hons' - and I'm unsure now as to quite what the correct terminology should be - does it depend on size?? Some of these things get to be quite large I understand.
2).......I haven't yet tried Boyd Rosie, as believe Christine is correct, and my sources also say that pieces from that factory should be marked. However, I may try Boyd.
3).......Have looked again at the glass, and regret that in the flesh it doesn't appear yellowish, so apologies and maybe my camera work at fault. It has a general white clearness.
4).......No reason to think the top and bottom are mis-matched Rosie.