The information at the McGimpsey site shows a way to do this with .txt files
and a way using the registry. Since you have two different series going,
you'll probably want to use the .txt file solution.
Also, his method is based on invoice numbers being actual numbers, but for
the format you have you'll need to look at combining numbers and text, or
converting number from the text file and then formatting them as text with
leading zeros so that they appear on your invoices properly.
If you need assistance with that type of thing, feel free to post back here
or even to contact me at (remove spaces) HelpFrom @ jlathamsite.com