Corrected entry: The film starts around November 13th. Then Henry takes a long time to get Lucy's attention in various ways etc and the movie is called 50 first dates, so you'd think at least 50 days pass along with the days where he doesn't succeed with her. Shouldn't there be Christmas decorations or something similar? It would be safe to assume that Christmas would be very close by the time Henry is ready to leave.
Corrected entry: When Henry is pretending to be tied up, Lucy's father drives by and tells him to go to their house. When Henry gets to the house, Lucy's father tells Henry that he's figured out that she only sings on days she has met Henry. It then shows her singing. She hasn't met him yet that day, so why is she singing?
Correction: Although it is possible that this is is a plot hole, it is also possible that Henry did indeed see Lucy that day. There is an unshown period of time when Henry is untied and eventually makes it to Lucy's (father's) house. She may have indeed seen him that day, and been the one to untie him.
Correction: No there shouldn't be decorations, because they don't want Lucy to find out what happened. Also, the movie is called "50 First Dates" as a way of hinting at the plot, it doesn't literally mean there is 50 first dates. And, even if it was literal, they obviously skipped many of the days to cut back on time, so the holidays were left out intentionally.