In short term, if you’re not seeing good shedding 2-3 weeks after each treatment, then it’s a sign that you’re being under treated. But if you don’t start seeing significant reduction after 4 treatments, then you can tell that laser isn’t working on you (again sign of improper settings.) Laser on legs doesn’t require 20 treatments. 6-8 treatments max!!
No body hair should take more than 8 laser treatments. If you have hair left after 8 treatments then it’s the best reduction you could have achieved with laser assuming all of your treatments were aggressive as possible.