This is true of me as well. I started with C++ in 1991, and I generally knew the language spec quite well (as far as users go) up through C++11.

But now the language packs so much complexity that I can't be sure I understand all of the code I'm looking at.

My usual quality standard for production code is that it doesn't just need to be correct, it needs to be obviously correct. So that's a problem.

Doubly so when the other programmers on the team aren't C++ geeks.