The problem there is the lesson numbers need to be displayed in the course platform's UI.

I can't have my course's lesson numbers be increments of 10. It's too confusing for end users, and they also can't be different than what I have on file because then it would be a nightmare to maintain (as the person who created the course).

Using gapped numbers is a great way to solve certain ordering problems though. That's a common thing to do with database position columns for ordered content.