RORY: But how are we going to go to four Thanksgiving dinners?
LORELAI: It’s not four, is it?
RORY: Lane’s house, Sookie’s, and we always stop by Luke’s . . . that’s three, and Grandma and Grandpa is four.
This episode’s plot is laid out here – the Gilmore girls have to eat four Thanksgiving dinners. Rory’s statement makes it seem as if they usually have three Thanksgiving dinners each year, but somehow a fourth Thanksgiving dinner is a step too far!
The Annotated Gilmore Girls 