Do the add-ons for recent killers stack?

TomTheSequel

I've noticed that the 'stacks' in the description of all the recent killers don't have it. I just wanted to know because I want to use certain plague add-on combos but I don't want to waste them if they don't stack

Boss

https://deadbydaylight.gamepedia.com/Add-ons#Stacking

This should help clear things up.