Yeah, some provinces give a valor bonus to more than 1 unit, but it will only ever display the first one. I think Bulgaria gives bonuses to two (Bulgarian Brigands and either Janissary Inf or JHI, IIRC) as well.

Spies for me are mostly peacekeepers within my own lands, but they can be good for softening up a soon-to-be-acquired territory or betraying an enemy castle. You can train them up before sending them on foreign missions to increase their survivability. Some of your options are: 1) building higher-level spy buildings 2) keeping them in your territories but not building border forts (without the BF it's up to your agents to catch enemy spies and assassins, and when they do they increase in valor) 3) try a crap unit, ie peasants, for treason over and over again. When they get spy-resistance virtues, disband and train a new one. Before long you can have a network of 5-valor spies to send abroad without having exposed them to any danger in the process.

Ajax