The best thing to do is to give Armor Digimon levels in the context of each game, usually equating them with the Adult level. There are many instances, for example, in which a Child Digimon evolves into an Armor Digimon naturally as an "Adult" level. I believe Drimogemon, an Adult, evolves into Digmon in Savers (possibly in an example of slide evolution but we all know that evolution in Digimon doesn't have to necessarily mean moving up). This could also mean that this Digmon was comparable to a Perfect level Digimon, though.
So no, let's not have a set standard for every single bit of Digimon media out there that goes so far as to give Armor Digimon a specific level ALL THE TIME.