Since this is turning out to be a very controversial answer and I feel I could have done a better job writing it, here's the question, answer and correction:
Q: Ask Marin is it truly worth training skills past 20? Ie 20 OD VS 23 OD
A: -I'm dangerously close to revealing too much here but personally, I'd say no, it's not. There might be specific situations where this might give you that "edge" that gives you a victory in a very close match but these are super rare.
Correction: The simple answer is that there is a noticeable difference between skill level 20 and 23, so yes, this training will not be in vain, especially in at highest levels of competitions (NT matches, etc...). As levels progress, differences between them become smaller and smaller but still, there are differences!
Hope this clears things up at least a little bit.