Corrected entry: When Jen and Dawson are talking in the darkroom while developing his photos, Jen says, "The way everything went down last year. You know, how you found out and all", referring to Pacey and Joey's secret romance. However, Pacey and Joey didn't become involved until well into the Spring, and just before that same Summer. So it really wasn't last year, it was just a few months ago right before Summer break.
Corrected entry: When Bessie is questioning Joey about what happened while she and Pacey were on the boat for the summer, Bessie tries to get Joey to tell her whether or not she slept with Pacey by making reference to the fact that Joey left her high and dry last year. Joey left last season (season 3), which was 3 months prior to this episode, not last year.