CA: question about frighten effect/germans

[Dorkus]

Do frighten bonuses stack, or can a unit only be frightened only once?

I ask because the germans have 4 separate units with a frighten effect: night raiders, berserkers, warhounds, and screeching women.

Thanks

PS Actually, any additional details you can give would be nice as well.

For ex: 1. numerical value of frighten effect; radius; level of morale necessary for unit to rout (-6 in mtw?); any other penalties units face ude to low morale.