There is an issue somewhere that I haven't found. I'm not even sure if it is still present but at some point, the skills from Northend all become "known" for my toons. You find this information in the by character SaveVariables.
In order to fix that, I've added the following in my local version.
In TrainerFu_VisitTrainer.lua, at line 145 for me :
if knownStatus == "used" then
self.db.char.knownSpell[skillFullName] = true
-- New section to mark skill as not known
elseif knownStatus == "unavailable" or knownStatus == "available" then
self.db.char.knownSpell[skillFullName] = nil
The net result of this bug was that until I did my fix, it looks like TrainerFu wasn't learning any of the new skills when in fact it was learning them but was also flagging them as known by the characters so they ended-up not being displayed.