Incorrect Prior Amt on Progress Bills

I was spot checking a project's invoice when I noticed that it was invoiced at 150%!!!

When I asked the AR staff how this was possible, they said it was the only way they could get the invoice out for the correct amount.

When I looked at the project's billing profile it showed a prior billed amount of $1852.50 invoiced on a total estimated amount of $1,235.00.

When I looked at the project's transaction history, I only see the estimate for $1,235.00, an invoice for 50% of the estimate of $617.50, and a payment for that invoice for $617.50.

Somewhere the system is counting a third invoice that is not present.

When I asked the AR staff if they had created another invoice and then deleted they said that they might have done that. 

When an progress invoice is simply deleted instead of voided, is that what creates the prior billing tracking overstatement?

I need to confirm this is what is likely causing this error. 

If it is I need to make sure the AR staff doesn't delete progress invoices when they find an error and instead void them.  Then I need to figure out how to fix the ones that have this error.

Can anyone shed some light on this?

Thank you.