QB Issue Resolution:

Sure – you just select them in the register and choose Edit->Delete. Or you choose Edit->Delete on the form itself (invoice, etc).

One caution I have though is if you used these values in calculating your taxes, deleting them will result in a difference between your books and your tax return. For that reason I try myself to reconcile everything completely at least by year end (well, at least prior to sending in taxes).

I suppose the correct way to handle this is to fix them and submit a correction to your taxes.

Resolution for Issue 'When you have some unreconciled transactions after a year of reconciling, is there a way to delete/void/eliminate these, since they must be a mistake?' available: Yes (Solved).
Source: Intuit Community forum.

When you have some unreconciled transactions after a year of reconciling, is there a way to delete/void/eliminate these, since they must be a mistake?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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