It’s not possible to add the data to the queues with the same reference, you will get error like duplicate reference while adding same to queue if you checked the unique reference option while creating the Queue.
If you haven’t checked unique reference while creating queue you can add the data with the same reference for sure, it doesn’t throw any error.
If Queue Item fails you can Retry it from Tenant > Queue > 3 Dots > View Transaction Items → 3 Dots > Retry Item
A new item will be added with same data and unique reference. The same happens when you set the Auto Retry option… a new item will be added with the same information (include unique reference) automatically when transaction item fails with system exception.
If you need add the same reference overtime like employee-id is better disable unique reference or you can concatenate with something that turn it unique like employee-id-datetime, employee-id-month etc