The executed version, any dated amendment, the notice that delivered it, and the signature pages tying the investor to a specific text. Also keep correspondence describing the change. If a later government notice describes the arrangement differently, treat the discrepancy as something to investigate rather than something to accept or ignore.
Keeping the record of what was agreed
Version control sounds clerical until two texts disagree about when money moves. Build a short chronology: date of the original subscription package, date of the amendment, date of signature, date of release. Where a representative said something at a webinar or in an email that differs from the document, keep it — public and oral statements can carry legal weight, and deciding on your own that they cannot is a poor assumption to make.
The file should connect lawful accumulation with the actual path of the invested funds rather than treat either document as the whole explanation. Keep the real dates and figures rather than presenting a simplified version.