They do not. With regards to Milae's situation, there is a different promotion that gives something with the same name. Don't remember where it counts from, but I think it's temporary.
There is the special Moral event on one hand that gave a temporary version of the promotion that stacked with the permanent one. On the other hand, the Scottish custom civ also gives access to a UNW that gives temporary stacking combat bonus when liberating a city or unlocking a policy.

