Hancock and Strong don't respond to the some of the companions they are replacing in their pickup scenes. The lines are there in the Creation Kit. I noticed this on multiple playthroughs, and there are youtube videos of these scenes that also show this. I believe I've figured out why.
Quest COMHancock - COMHancockPickUpScene
Hancock he doesn’t respond with his line for Curie, Deacon, Piper, or X6-88 in the pickup scene in the quest COMHancock.
The lines are there in the Creation Kit, but they seem to be set up wrong. For the characters his response works for, the GetIsID on his line runs on "Quest Alias: Companion" - for the ones it doesn't, it runs on "Target".
I tried to fix this by changing “target” to “quest alias: companion”, and the lines now play for Curie, Deacon, and Piper. I don’t have X6-88 in my usable save, so I can’t check with him.
Quest COMStrong - COMStrongPickUpScene
Strong's response to Curie when he's picked up doesn't play. It seems to be caused by the same problem as Hancock's pickup lines. I tried the same fix, and he now says his line.