Depends:
The older and more sandblasted barrels get, the more and more vigorously they need to be cleaned, from my experience. I just took off a barrel that was half way through it's 6th season and it needed de-leading after every match and to be cleaned after every card, to be competitive.
From my experience, as barrels age, the x count will fall off abruptly after 50 shots or so. They never shoot better than they do right after they are cleaned to where there is no black on a patch and a few foulers shot through them. Some try to play the leaving some fouling in, I guess to save on ammo but one thing is for sure, one can duplicate the results from Spotlessly clean, the rest is guesswork.
I am down to using a Lewis Lead Remover type device in my Sporter to keep it shooting somewhat competitively but it is about to get a new Ratchet, as soon as I can cut a crown that suits me.
Pete