Matthew Boulton goblets?

I picked up these yesterday for £4.99 each. Google says they are early 19th C Matthew Boulton. The amount of wear would suggest that they do have some age. The engraving has me perplexed though. 'Christmas 1975'. If they are a fine antique why would someone do this to them?

 

Sigh - one reason engraved dates aren't always an indicator of correct age, they may or may not have realized their age or value. Regardless, even with the engraving and quite a bit of bleeding, still nice Old Sheffield Plate and lovely to have a pair...

~Cheryl

 

Maybe they didn't. It might have played into my hands though, in that maybe the charity shop i bought them from were swayed by the engraving when pricing them up. I nearly didn't buy them. I thought they were Moroccan when I first looked at the mark.

 

I'm going to try and clean the excess polish out of them and leave it at that. Not much silver left to polish.

 

I've had the idea that Sheffield Plate was silver, thicker than foil, bonded to base metal.
So I have a puzzle about how that could have been so worn or polished away. Please forgive my ignorance...