Some things we let go, for example forgetting to collect your income or place your units. We try to stay on the honor system as much as possible - because whats the point of playing a board game if you intend to cheat to win?
As an aside, things like not “seeing” something or mis-identifying something after you end your turn is subject to the situation. Forgetting to move ships to protect TT… tough luck you lose your TT. Not realizing that aircraft are bombers - tough luck and good play on your opponent.
But things that generally don’t impact unit losses like NCM AA guns forward or taking an obvious move such as forgetting to NCM that 1 Inf you didn’t use to take Bulgaria on G1, which was an obvious move that was setup in the combat move - we generally let go.
Of course, if we notice something after the fact when die have already been cast and it would impact that battle - generally tough luck.
A HUGE part of this game is attention to detail, particularly in strategic moves. I’ve found it best to stop before you end your combat moves and again before you end NCM moves to step back, grab a drink and scan the board. You’d be surprised what you catch if you stop rushing - intentionally or not.