How do you handle resistance to non-magical attacks of old stat blocks when trying to work with them in the new 2024 rules?

We are in the middle of a campaign that we started years ago, and we as a group decided to switch over to the new 2024 rules. The problem I am running into now is that the monsters wanting to use that old resistance to any non-magical bludgeoning, slashing, or piercing attack damage. In the stat blocks they did away with it and either they are resistant or not, magical attacks be damned.

So how do you parce this? Do you just assume it is all non-magical and apply resistance or do you assume all the damage is magical and do away with the resistance all together?