Continuity mistake: Marshall tells Lily that he has never been to the ladies' room of the bar. However in the second season episode "Showdown", Robin catches Lily and Marshall "holding hands" in there. And in "Of Course" in season 5 Marshall, Ted, and Lily go in the ladies' room to comfort Robin.
Continuity mistake: We find out in this episode that Ted and the mother don't get married for several years, due to postponing the wedding when she became pregnant. They eventually get married in 2020, when their children are 3 and 5. But in Lobster Crawl (8-9), at the end of the episode Lily and Marshal show up to babysit Ted's daughter when she's younger than that, and Ted is wearing a wedding ring.