I have always considered the rule book to be the definitive resource when there are disputes. What you might consider "Universal" may not be viewed the same by others.
Like you, I have always considered it an act of concession but if my opponent disputed my claim I would have to defer to the rules.
My opinion against someone with a contrary option does not afford me the higher ground. The rules always prevail.
If it were truly universal.....it would be a rule and there would be no dispute....in much the same way we recognize that if our opponent scratches, his inning has ended...It's a rule.
Keep in mind, there is no universal rule book regarding pool. Every league has their own rules.
Well, I ain't no tournament guy, I ain't no league guy, I'm an action guy. I can assure you in most places if someone unscrews while you go to shoot it is concession. If that is contested, there WILL BE A FIGHT. It's not in any rule book, it's understood - it's code.