I understand what you say about WP Super Cache, but only yesterday someone reported a problem with their site, and it turned out the problem was with W3 Total Cache, which they had been running on their site for quite a while.
Updates to plugins change things, and that applies to caching plugins as much as any other. (Actually, from looking at the forums for W3 and WP Super Cache, updates are a frequent cause of problems for those plugins).
So I would still check.