Check with your State Board of Financial Insitutions or BOL members in the state where you work.
In the states where I work, minimum retention requirements of bank documents is outline in state code and are inclusive of Commercial Loans.
For Example - Credit files, appraisal,applications, etc. are to be retained for 5 years after loan closes (Commercial and Consumer Loans).
Regarding the prior posters reference to denials - 25 months (after the credit decision is made) is a Regulation B issue and includes small business with annual revenues of $1 million or less and consumer loans.
So depending on the state in which your bank operates, the answer will vary.