It does indeed mean what you have surmised.

Personally, in this sort of situation, I prefer to use 'no.', as being more universally understood; as you say, in EN we sometimes also say '2 off' etc. — but this seems to be a source of some confusion with certain readers, and is so perhaps best avoided.

I have been using 'no.' (= number) in this sort of context for many years, and my customers seem well satisfied with that solution.

One might also consider 'qty' (= quantity) — but personally, I always feel that reads rather awkwardly if in your mind you 'expand' it to the full version on reading it in your head, so I tend to avoid that option.