I do not reconstruct from what you remember
Owners tell me the business "did about $800K" in a year they never closed.
That is not a source document. I rebuild from bank and card statements, invoices, and third-party payouts. If it is not in the records, it does not go on the P&L as a fact. It goes on a gap report.
That rule is why book reconstruction for tax deadlines can survive a preparer, a lender, or a buyer. Memory cannot.
Why the bank is the starting point
BLS describes bookkeeping as computing, classifying, and recording so the organization keeps complete financial records. Complete records start at the cash movements.
IRS recordkeeping guidance is the other half. You need to support the return. Bank statements are usually recoverable even when QuickBooks is not. I covered dead files in dead QuickBooks file reconstruction.
Order every account, every month in the gap. Then we categorize against those statements. Then we reconcile. Then a licensed CPA reviews the file.
What a gap report is for
Missing months. Closed accounts. Cash a client swears existed. Personal cards mixed with the business.
Those items get documented with dollar amounts where we can see them, and marked unsupported where we cannot. Your preparer decides how to treat them. That is also the subject of missing records and bookkeeping gap reports.
We do not smooth the P&L so it looks like a year you wish you had.
Same statements monthly. One set per rebuilt year.
Sample deliverables is a monthly pack: P&L, balance sheet, reconciliations, reasoning log. Reconstruction uses that same set for each year we rebuild. Catch-up vs monthly explains why you should not buy a monthly seat to hide a historical hole.
CPA firms delivering this under their brand start at For CPA Firms. Pricing is a $499 diagnostic, then a fixed quote. Nothing recategorizes until you approve the number.
The Journal of Accountancy's guide to structuring outsourced work still applies here: review stays with a CPA. Production is not the same as a guess in a spreadsheet.
Pull the statements. Then talk.
Get a reconstruction quote once you can send records, or start on tax deadline reconstruction.