I agree some form of versioning of out going documents is of value. A date of generation makes most sense to me as it provides some stand alone auditing information.
I also agree there is value in having an exact copy of documents sent to external parties for precisely the type of issues you describe. Manger may create reports dynamically but the copy of the report in the external partied hands is not dynamic, they have now obsolete information.
I address that by saving out going correspondence as a pdf then attaching it to the financial transaction. Not ideal but the best I could do atm Feature Request: Report Snapshots - #17 by Patch
For standard document the history button can be used to identify past changes.