During the pagan ritual, Sam was cut on his right arm, but at the end of the episode the bandage is on his left arm.
Santa's red suit is not so much part of the lore as it is successful marketing. His suit had no definitive color until Coca Cola started showing him in red and white to match their colors.
During the flashback scene of 1991, Dean is seen thumbing through an issue of hotrod magazine. The magazine used is the November 2007 issue, and a red S197 Mustang is seen for a brief moment. This body style of Mustang was not released until 2005.
Sam states the Jesus's birthday was most likely in the Fall. While some scholars have agreed that the census Herod required was conducted in the Autumn, some scholars have guessed that Jesus's birthday would have been in Spring, probably March. However, there's no exact date, agreed by everyone
The second time Dean's arm gets cut, the blood drips away and you can see that there is no cut.
In the flashback, young Sam and Dean are supposed to be in Broken Bow, Nebraska. But through the motel window, can be seen the sign for the Cicero Pines Motel, which is from the 3.2 episode 'The Kids Are Alright', set in Cicero, Indiana.
While Sam and Dean are exploring the basement, they discover one of the victims still alive. They are attacked and captured. Eventually they escape, and slay the demons, but the man alive in the basement is never mentioned again.