Final answer:
The most challenging type of misstatement to uncover is fraud concealed by non-recorded transactions because there's no direct evidence of the transaction.
Step-by-step explanation:
The most difficult type of misstatement to discover is fraud that is concealed by non-recorded transactions. This type of fraud involves not recording a transaction that should have been accounted for, making it challenging to detect since there is no evidence of the transaction occurring in the first place. In comparison, over-recorded transactions, transactions recorded in subsidiary records, and transactions involving related parties leave a trace that may lead to the discovery of the fraud.