Please Explain NGC Numbering System

The first part of the number is the number on the invoice. The last three numbers are coins ON the invoice. So for invoice 1234567 the first coin is 1234567-001, the second is 1234567-002 and so on up to 1234567-999. You can't have over a thousand coins on one invoice. If you do send in over a thousand on one invoice when it gets to the one thousandth coin the computer goes out and finds an invoice number that hasn't been used yet say 1727383, and the thousandth is is 1727383-001, the 1001 coin is 1727383-002 and so on. Some people use photocopies of invoices that they have. This means several different invoices with the same number, or in the case that someone uses an invoice whose number has already been use, the computer assigns it a new unused number. The one thing I've never understood about this is what happens when someone goes to look up his submission and uses the numer he sent in, but the computer has assigned a different number to it. He would see someone elses submission. I could see that causing some panic.