@lubos i would request you to add a Last Updated column to all transactions for every tab.
the column would automatically show the date and time when the transaction was last edited.
it would be an additional bonus to users if while editing a transaction there was a field to enter the reason for the edit as well and preventing user to update without providing a reason. this field would appear only when updating a transaction and not during initial creation.
this would also help in improving the audit trail feature which you are already planning to improve.