The original approved file, plus a running record of the business: financial statements, payroll registers, leases and their assignments, equipment schedules, customer contracts, and the share register. Renewals are argued from these, and reconstructing several years of operations shortly before an application is both expensive and unconvincing.
Keep the business file as if it will be read
Investors keep excellent records for their accountant and patchy ones for anything else. The renewal file needs a particular set. Annual financial statements, prepared consistently, showing revenue and the investment on the balance sheet.
Payroll registers by period, because headcount over time is the strongest evidence against marginality. The lease, and any assignment or new lease, with an explanation of any move. An equipment schedule, particularly where the purchase price was allocated across assets.
Customer contracts or a customer list showing that the enterprise is real and operating. And a current share register, since ownership is a continuing condition and shares change hands more quietly than anyone expects. Where a substantive change has occurred, add a short contemporaneous note explaining what happened and why, prepared at the time.
That note is worth more at an interview than a reconstruction offered three years later.