A transaction has more than an amount
Two deposits of the same size may come from different sources: a customer payment and a transfer from another account. Preserve the information explaining each transaction rather than classifying it from the bank line alone. When preparing a working ledger, leave a question marker on any entry whose source or purpose remains unclear.
Build a source link
Attach an invoice reference to a customer receipt, an account explanation to a transfer, and the relevant supporting record to an expense entry. Include the tax period and document date in your index. If a receipt covers several items or an expense serves more than one purpose, write that complication down for qualified review instead of silently assigning a convenient category.
Keep the boundary through later summaries
A high-level income or cash-flow summary should point back to this source work. Keep the original ledger and any corrected version distinguishable, with notes explaining changes. These boundaries help prepare a tax discussion but do not establish the tax treatment of every item. Ask which unresolved classifications need additional records or professional analysis before the figures are used in a filing or account submission.