In principal I see what you mean, but it will be of limited benefit because many entries contain more than one alternative number. What you have said is that you will be basing your choice of alternative on the newest, where there is more than one. Once an entry has been verified, it isn't checked again. So it's down to visitors to report numbers that don't work. If some (older) numbers don't work and aren't tried by visitors, then they will remain forever.

IIRC the idea of ratings has been mentioned on here. But again, there are often several numbers per entry and if there were to be such a scheme, it would need to differentiate between numbers else those working on the database will have to check each number.

I think that the best way to report a number that doesn't work is to put another entry in the database with an annotation in the 'Other Information' field. In some cases the geographical number has changed and there is an announcement saying that it has changed to another geographical (perhaps when a company has moved). In this case, all it requires is for us to amend the entry with the new number. Simply giving the entry a "thumbs down" would not convey to us that there is an announcement. That's why a new database entry with something along the lines of "This is the new number given when you call the old one."