Hi tmushang!

Welcome to the Community! Thank you for asking about a warning for a duplicate bill number. I'll be happy to share information about this.

The only warning of QuickBooks is for duplicate bill numbers from the same vendor. There is no warning that a certain number exists on other vendors’ bills because eventually, one vendor may provide one that has already been used by others.

On the other hand, I know you have your reasons, so the best thing we can do is to run the Transaction list by vendor report and filter the bill transactions. The export the report to Excel and sort the transactions by NUM to easily find the duplicates.

I'm just around if you need assistance with your bills. Take good care always!