So, both Gadgeteer and Commando have Armor Master and Improved Armor Master, and while it's obvious why it doesn't mention if it stacks in the EotE core, AoR doesn't change the description. So should it be assumed that having two of Armor Master, and likewise Improved Armor Master, don't stack?

Armour master is not a ranked talent so you can't have it twice. Once you buy it on a talent tree you have it across all of them.

Armour master is not a ranked talent so you can't have it twice. Once you buy it on a talent tree you have it across all of them.

^ what That Blasted Samophlange said.

Armour master is not a ranked talent so you can't have it twice. Once you buy it on a talent tree you have it across all of them.

Yup, and as soon as you've bought your way down to it on the second tree, it unlocks as if you had just purchased it, so you can purchase right on past it