Paul,
Having asked the question, I now have both goblets together probably for the first time. The known one, Q 16 4 M, when looked at in a fresh light has the same sort of 4, the Q, could, if you did not know it, may be mistaken for an 8, the 16, if viewed upside down, does resemble the "2", and the "M" is very indistinct. It is only from having a picture of this that I know it is Q 16 4 M. Thus it may be possible that the mystery goblet has the 16 upside down, with the 1 a bit vague. Leaves the "I"/"1" to be the "M"!
Furthermore two goblets were registered on the same day, 274962 aka Q 16 4 M, and 274963. I am suggesting that this mystery one may be 274963. And they do have an indisputable similarity. Can you or anybody else confirm this?
NosLoz