Yep old comments that not in a sync with a code is a big problem. For some reason many developers even seniors when making update forget about updating the comments. Especially this is a pain in the ass when this comments used to build API docs for code. In my practice i kill so much time on bugs that was caused wrong documentation. And i saw this in Microsoft, Google, PayPal, Amazon, etc. So this is not problem that exist only in small and bad maintained projects.