Here's a great example from 1981: the numbering on SPIDER-MAN (also, at that point, providing temporary accommodation for THE INCREDIBLE HULK and refugees from the short-lived MARVEL TEAM-UP weeklies) suddenly jumps from issue 427 to 429. And then remains 429 the following week. Whoever was responsible for pasting-up the cover box (a London production function since '79) boobed. Oopsie!
So, although there isn't ACTUALLY a missing issue (Spidey's weekly ran a commendable 666 issues), anyone looking to complete their collection with issue 428 will have a long hunt.
I think this mistake was acknowledged in a latter Spidey letters page.
13 May 1981
20 May 1981
27 May 1981