If I know pages are missing - I may or may not buy the magazine. I can look through it and see if there is enough left for me to want to take it home.
However, if I find that a magazine or book that I expected to have ALL the pages in has missing pages - I am disappointed (I don't think QB will let me say what I am really feeling!)
I think if you donate with a sticker on the cover saying "some pages missing" - then the buyer or taker will be aware.