Sorry, I skipped to the end. I'm bad. But, jeeves:
The suggestion that Glamis is an obscure name in English literature is bizarre. Macbeth is one of Shakespeare's most important plays and Glamis is one of the name character's titles - the fact that he is Thane of Glamis, becomes Thane of Cawdor and it is predicted that he will become King is its central theme.
That is not a 'theme'. I'd be more worried by someone who can't distinguish a plot point and a theme.
If you are interested enough in English to do an English degree and become an English teacher where your job is to teach and inspire young people, including in relation to our greatest playwright
Some of us have gone to university post-1880, and no longer accept the 'our greatest playwright' line, as it's very very dated.
Also, if you have learnt anything about Shakespeare you should be aware of metre and that "Glammis" simply can't work.
If you have learned anything about Shakespeare, you should be aware that his metre is extremely slipshod in a lot of places and an extra unstressed syllable is neither here nor there.
Anyway. I don't see how it matters. It's not in any way important to understanding the play (not like the thread a PP mentioned where someone thought P&P was Victorian). It's just a slip. Shakespeare made loads of them.