In the recorded lesson for ninth-year accounting students, the teacher discusses potential errors in the trial balance, emphasizing that even if the trial balance aligns, errors may still exist in the accounts. Examples include omitting transactions entirely or recording them incorrectly in the ledger, which could lead to discrepancies being discovered later when, for instance, a supplier contacts about an unpaid invoice. The lesson highlights various types of errors, such as omissions, duplications, and misposting of entries, underscoring that routine checks are essential to avoid these common pitfalls in accounting.