"If you've learnt to understand it, why do you assume others will be unable to?"

That was not the point. Where this got started, I said that !!$return is a bad idea. The statement essentially returns a flag (boolean) value. Some prior statement should have made to make the return value crystal clear and given it another name other than $return: like $all_accounts_valid or whatever fits the application.

So the first style point is that $return doesn't describe what it is. Yes it is a return value, but what kind of return value? One line of code before the return was needed in my opinion to turn this into a boolean return value.

If you don't agree that using a better name than $return is "easier to understand" and a better style, then things degenerate from there and I have no hope of convincing you otherwise. And yes this will require one statement before the return to make this clear. But..

return $all_data_valid; is better in my opinion than:
return !!$return; There is no need for this confusing !!$return.

This is not a point of whether !!$return can be understood, the point is that there are easier ways of expressing this idea so that it can be easily understood. A Perl return scalar doesn't have a type declaration like in C. Often that very last return line has a lot of contextual meaning. returning a flag like: $all_data_valid is just going to convey more information than !!$return.