Go to the bottom of the base and go to the spot for the UNderground, Last Stand and Survival. If you can go in there, then you have them and they are installed.
For Last Stand, Benitez should be in your ear constantly about "Going to see Kekich"......
Also, you will get alerts for supply drops in the city.
On this week all 3 DLC works now well.....¯\_(ツ)_/¯i bought all DLC's but i dont know if i ever installed them ,i just find info i own them.
Screenshots from DLC Underground
https://forums.ubisoft.com/showthrea...1#post15148167