It's love that makes them faithful I think. more than anything. Both my dogs came to me after puppyhood....the first at 10 months/1 year (never was exactly sure)....the second at three/four (?not sure with her either) They have both been the most faithful dogs.
We have a friend (dog) who visits us. He doesn't even belong to me! But he remembers us, loves us like crazy, visits us regularly, never forgets....I call that faithful.
That is a hard one apart from Shane my Golden Ret who I got at 9 wks.
I have two Clumbers Oscar and Maybelle Oscar at 10wks and Maybelle at 12 months Maybelle( the one you call a Sheep... Labra) took a while to settle in but between her and Oscar really there is no difference ! Maybelle loves her sleep she does not get out of my Bed untill about 10 am its a dogs life I tell ya lol.
Saying that!! if it is a rescue dog so different.