How important a buffer overflow is and what you can do about it are entirely application dependant. In one application you might not want to use valuable CPU time to check the buffer, in another it may be critical to know if the buffer is corrupt or even to prevent it by dropping data and telling the app that it happened.
"Flags might help find it."
BINGO!!! Even if buffer checking is not appropriate for your app in the field, it can be a valuable resource for debugging.
Not sure what that means, but the important thing is to know if data has been lost so that something can be done about it even if that is to not trust the results produced from the data or turning on a red light and shutting down!