Depends on the mod
GWX has changed a couple of things such as correcting the dates for Flower and Hunt DD as well as a few other ships
Missions written for stock may include those ships at an earlier date
Plus some ships have had the names changed or type ( Scharnhorst one example from a BC to a BB ) so the mission will crash
I know before every GWX update I have to go through them all to make sure are ok
I miss the odd one
Have just done them all for 1.04 plus a lot of the older ones knocking about
There are quite a few at UBRS in the Download Central
Got a load from there the other day