The problem is that 1) PCs aren't that old, 2) they haven't devoted the years and decades to learn it, 3) they aren't specializing in monster knowledge, they are specializing in their class, and 4) knowledge isn't accumulated in D&D as it is in the modern world.
There's no way that a PC could be that good. So no, your claim is not correct from a realism point of view unless the PC is some sort of non-combat sage class and doesn't adventure, but rather just studies at libraries and/or colleges, talks to peers and writes papers on the subject.