Where is the limit on the amount of armory traits a class can take? Properties are limited, as are which armory traits a class can use by properties; however, I don't see a limit on the number of armory traits.
Perhaps it's a wording thing. It the discipline penalty just supposed to be X-1, where X is the mercenary trait value? Humanoids -> Environmental -> Cultural -> T2 seems to be the only place it's used. There it is Mercenary Class 2, which seems to always give a -1 to discipline based on the Core book sample army.
Based on the example in the Core book, you count the merc trait in addition to the 2 armory traits you can take such that this 1 trait counts as 3 total for determining the amount to reduce discipline.