Letters from Belastingdienst

Action: only in the if unlikely situation that the information that the Dutch tax authorities took from the employer's wage tax information is not correct, you need to inform them.

You will receive this letter in case the information in the income tax return does not match up with the information that the Dutch tax authorities have received from Dutch employers, Dutch financial institutions and/or local authorities. 

In page 2 they mention which information they received (usually wage tax records).

In general, the information that the Dutch tax authorities have in file are correct, even if the amount differs from your annual earnings statement. In that case it does make sense to double check with the Dutch tax authorities.