Label the account before filing the document
Identify the person or entity, tax period, and authority communication involved. Keep a return copy and its supporting records within that identity rather than combining every paper by the date it arrived. A transaction affecting more than one area may need a cross-reference, but it should still point to its original source. Do not decide a payment or expense’s tax treatment simply from the folder where it is stored.
Use an index to explain the relationship
Record why a document may be relevant and which question it supports. Keep personal identifiers and business information secure, and clarify what a proposed reviewer actually needs. If a file contains records from different authorities or periods, make that distinction visible on the cover and in the index. Retain the version supplied for a particular review so later follow-up can refer to the same evidence. The separation method supports preparation; it does not determine filing obligations or establish that two accounts can be handled through one process.