I deleted a couple of my replies. Luckily, no one saw them before they were gone.
Basically I think the page ennumeration allots pages based on total comments present while the page assignments are static and are based on all comments made. You could end up with a scenario where Page 1 has 19 comments (1 deleted), Page 2 has 17 comments (3 deleted) and Page 3 has 2 comments, for 38 total present comments in the thread - therefore only two pages will selectable.