Sales Invoices Numbers

SUGGESTED

Why is it when I've sorted the customers names in alphabetical order and then print the invoices the customers do not remain in alphabetical order.  Therefore, the invoice number that is assigned to the invoice is not in order.  This makes it very difficult to import receipts when matching the sales invoices by invoice number.

For example, 

Last Name

Invoice # Assigned

Should be Invoice #

A

1

1

B

5

2

C

2

3

D

7

4

E

9

5

F

3

6

Does anyone know how to fix this?