: So, GURPS is canon.
: Myth III is not.
: I think that's the conclusion.
It really depends on how you define canon. The way I see it, while Myth3 may have had less Bungie involvement, it is nevertheless the third official Myth title, which has to count in its favour.
And I think we can put the reference to "a" Tain down to Connaught being an ignorant barbarian.