The Finale - S8-E23
Continuity mistake: When Leo opens the door and finds Grace sitting at the table eating chicken, the scrunched up ball of tissue on the table next to the plate disappears in one shot. (00:07:45)
The Finale - S8-E23
Continuity mistake: When Beverley Leslie is talking to Jack in the restaurant about him being his "associate", the napkin on the table which Karen left behind changes position a few times. (00:17:10)
The Finale - S8-E23
Continuity mistake: In Will and Grace's apartment, as Jack stands up to announce his news about Beverley, Will and Grace are cutting slices of cake and putting them on plates. In the next wide shot Karen (who is sitting on the sofa, away from them) had a plate with a slice of cake and a napkin, before Grace had even handed Jack any plates! (00:21:00)
The Finale - S8-E23
Continuity mistake: In the shots of the dorm hall showing Ben and Lila moving into their rooms, the two cardboard boxes outside Ben's dorm keep switching which one of them has writing on it. (00:31:25)
The Finale - S8-E23
Continuity mistake: Nearing the end of the episode, when Karen and Jack are sitting reading magazines, as Karen asks Jack a question, the way she holds her reading glasses changes between shots. (00:35:00)
Continuity mistake: Grace stumbles right after Karen says "Do you know how humiliating it was for me to have to finish myself off in front of your father?" but immediately in the next shot she does it again.
Continuity mistake: The 2 adapters on the back of the TV at the QVC set have their names covered up and not covered up, back and forth between shots that incorporate them. (00:08:00)
The Things We Do for Love - S10-E17
Continuity mistake: While Will and Jack are sitting at the table having a conversation, the mugs monogrammed "W" and "G" from which they are drinking tea magically switch between them several times. (00:06:30)
Factual error: When Jack is speaking to his mom on a mobile phone outside of his apartment door, he tells her that he will take her to Souplantation after she comes over that afternoon for a blowout. Jack's apartment is in Manhattan. Souplantation is a restaurant chain that only exists in California. (00:19:35)
With Enemies Like These - S11-E3
Continuity mistake: Sharon Timmer introduces herself to Grace in Series 10 Episode 1: "I've lived directly below you for 19 years." But then in Series 11 Episode 3 she seems to live in Flat 9B next door to Will and Grace. I'm not sure we've ever seen who lives there before, but guessing by the layout of Will and Grace's flat, there wouldn't actually have been space for an extra flat in that space. (00:00:16 - 00:12:12)