Well, probably the codebase doesnt have a lot of documentation, and thats why the 'top' engineers always tell you after-the-fact howto do it.

Next time when they point you to it.. Tell them: where was this documented. How can i prevent reinventing the wheel later?

Also ensure that the code that they wrote, is located in a logic location. Often it is not, and thats why its difficult to write in that codebase.

So it can mean two things: bad structured code, bad documentation, or you lack knowledge in the codebase.