It's not a simple answer.
There isn't a hard and fast written rule or official list that says they aren't valid. in fact in many places GW say it's your game play it how you like. It's up to you and your opponent what you agree to use as far as rules go. So, if you're playing a game against a friend, speak to him or her about it beforehand.
Having said that, most people tend toward a general accepted consensus. And the consensus was that since most warscoll batallions got a fairly hefty increase in points, and a lot of those that didn't get points going forward were for legacy compendium batallions, or in older versions of battletomes, so the assumption is that those are no longer intended to be supported by GW for their events, and many tournaments follow in what the bigger events do.
It might be worth checking to see if a particular battalion is selectable on the Warscoll Builder, or in the Azyr section of the Age of Sigmar app.
https://www.warhammer-community.com/warscroll-builder/It may be that if they are not on those list builders, then they are generally considered defunct