Hello johnskim9,
It's awesome that you've been using QuickBooks Desktop for as long as you have! With all this talk of the new year, it's really evident how long ago 2009 was. I appreciate your loyalty to the program!
I've done some testing using a 10-digit system like you describe, and I'm able to replicate what you're seeing. I've determined this is simply a limitation of the program, no matter what year and version you're using (for instance, I tried in a 2020 version of Enterprise).
Thankfully, you're able to save a transaction with a 10-digit number. Manually entering the next number in the sequence is the way to go to continue using this kind of numbering system.
I know this adds a little extra work and QuickBooks is all about cutting back on the steps you have to take. For that reason, I recommend leaving feedback for our product developers through the Send Feedback Online option accessed through the Help menu. Many of QuickBooks Desktop's current features were put into place because of feedback from users like you.
I'm here if you have additional questions. Have a great day!