Who is financially responsible when Quickbooks destroys information in previously reconciled accounts?

Hi @WIngwalker  , if you use quickbooks Online Accountant you have undo option for reconcile. In QBO you could remove "R" sign.

Unreconcile transaction

1. Go to the Accounting menu. Then select Chart of Accounts.
2. Find the account and select View register. 
3. Select the transaction you want to unreconcile.
4. Review the check column. If the transaction is reconciled, you’ll see an “R.” 
5. Select the box and keep clicking it until the box is blank. This removes the transaction from the reconciliation.
   
6. Select Save. Then close your register.

Here i give you article about unreconcile transaction . Cheers.

That is excellent instruction for matching transactions BEFORE reconciliation or for un-reconciling them before matching. Unfortunately I matched reconciled transaction and the result was chaos. I have yet to determine if it is even POSSIBLE to delete the some of the transactions that Quickbooks added to the ledger in the process. (I do not think any check I write can be listed on my ledger as a deposit. I wish it could be, but the bank has strong opinions on that sort of thing)

I'll help with your reconciled transactions, WIngwalker.

Yes, you can delete the transactions that are added when the reconciled transactions were matched. Here's how:

1. Select a transaction that you want to remove.
2. Click on it to open the transaction. 
3. You can also click the Delete button if the option is already available.
4. If not, click More at the bottom and select Delete.
5. Click Yes to confirm that you want to delete it.

Follow the same steps for the rest of the transactions. Let me also share these quick guides for additional references:

• Categorize and match online bank transactions in QuickBooks Online
• Fix issues when you're reconciling accounts in QuickBooks Online

The Community is always here if you need anything else.