One of Ted's unnamed cousins is played by Zachary Gordon, who also plays Grant, Barney's fake son, in season 4. If Ted's cousin was an actor, Ted would have recognized him at Barney's house.
When Ted ventures off to the Bronx to salvage a decorative Christmas that Marshall is soon expecting, an extra is standing behind him (black woman) as he's on his cellphone talking to Marshall, the woman then suddenly, starts walking off (as if action was yelled)
During the flash back to 1998, when Lily tells Ted that she always wanted an easy bake oven, Lily is seen wearing a pair of Puma Repli Cat shoes from 2006.
Since Robin was Ted' girlfriend and was staying in New York for Christmas, it is never explained why they weren't spending it together.
When Ted goes to visit his religious cousin in How Lily Stole Christmas, the little boy who plays the role of one of his cousin's kids is the same kid in The Stinsons episode, who also plays the role of Barney's son.
Zachary Gordon play the boy who is Ted's cousin son. Later on, in season 4 in the episode "The Stinsons", he also play as an actor who was hired by Barney to play as his son when his mother visit him and did not show any relationship with Ted.