terry wrote:But the allegiance you pick for traits must be the same as the artefacts etc. So you have a list building allegiance and a game allegiance. The don't have to match, as long as your army qualifies for the allegiances
That's not 100% correct.
You're only allowed to pick up the Grand Alliance allegiance abilities.
Armies that would qualify for 3 or more allegiances are not allowed to build toward one and then take the abilities from another, that is not the Grand Alliance abilities.
Example:
Slaves to Darkness all with Mark of Khorne (shared keywords on all units: CHAOS, SLAVES
TO DARKNESS, KHORNE)
Army list with Slaves to Darkness allegiance (with Knights as battleline) can only pick up the Slaves to Darkness or Grand Alliance allegiance abilities, but not the Khorne allegiance abilities.