They're not asking for any adjustment to the content, but for extra content, eg a feature piece that isn't tied to a particular date. Bear in mind that a full-page ad only covers one side of the paper so you need something for the reverse side, and newspapers are generally printed on folding sheets (ie 4 pages to a sheet), so that means 3 extra pages to be filled. It's not like the advertising department content is suggesting which content to use. Every newspaper has a variable pile of feature material whose exact publication date depends on the size of the print run, which is highly variable.

I'm curious about what you think the ethical breach here is. Advertising and editorial departments have to coordinate on practical matters like page layout.