I noticed an error in a set of entries a few months ago. What was recorded: - Sale was made for $X - Sale was made for $Y - $X+Y was deposited into Account A.
What actually happened: - Sale was made for $X - $X was deposited into Account B. - Sale was made for $Y - $Y was deposited into Account B. - $X+Y was transferred from Account B to Account A.
To correct the error, I deleted the deposit into account A (with two sales), entered two deposits into account B (one for each sale), and entered a transfer from B to A. The starting and ending balances for each account were therefore unaffected.
The problem now is that the reconciliation for that month is wrong. How can I put the new deposit and transfer into that month? I see an option to undo the previous reconciliation but not for an arbitrary reconciliation. Does this mean I have to undo and redo all the reconciliations since that time, or is there a way to edit just that reconciliation?
"The problem now is that the reconciliation for that month is wrong"
You don't have to Undo Reconciliations and redo them.
When you know the data still is correct, no matter how you changed transactions (one check should have been a Bill Payment check, or two Checks should be one check, or whatever), it should reconcile again just fine.
This is called Interim Rec or Mini-Rec. Use the most recent Ending balance and re-reconcile, ignore the beginning balance you see. That is the Net of all cleared transactions and you know you affected that Status. Checkmark them and you should end with the same ending balance as last time, if you really made no Different and just reworked the transactions.