What did you select on the Extra Keyboard Shortcut dropdown list in the History tab of the Customize dialog box? It doesn’t go to 11, 12, 13,… because a digit or letter merely represents shortcut key to access each item. There have been many questions about how these shortcuts are represented, so now there are three options:
I want one more if you’ll consider:
1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, …
How about this? Not only for shortcuts, but also for counting.