A funky merge like this (or a general delete/undelete)
can create a new page
id; essentially the revisions from the old page ended up getting migrated
from one page to another, and that other page now has the title of the old
page.
-- brion
Another case is when the old page gets deleted and a new one created.
Although they hold the same title, from MediaWiki POV they are different
pages.