That note about Loras and Garlan carrying three and two roses respectively when fighting together is rather interesting. I suppose that means that Garlan took part in the tournament at Bitterbridge? The lack of mention of him at all suggests that he wasn't.
No, Ser Garlan wasn't at Bitterbridge. Loras must just have decided to use the three-rose shield that day. I don't see Garlan as being as much a glory hound as his kid brother, so tourneys are not his thing.