Continuity mistake: When Doug sits down to read his book, he has his book on his tray. This then disappears as the shot changes. (00:11:20)
Head First - S1-E6
Continuity mistake: During the poker game, Arthur teases Spence because he's a virgin, which is mentioned later when Doug tells Cariie, "He teased him about the virgin thing." But in one of the later episodes, it is mentioned that Spence had an affair and had sex with his Home Economics teacher when he was very young and had long hair.
Fixer Upper - S1-E12
Continuity mistake: In "Richie's Song" Doug asks Spence if the M&Ms Spence found under the seat in the car are regular or peanut, Spence answers peanut, and Spence then eats them. In this episode, Spence somehow isn't allergic to peanuts. (00:08:10)
Continuity mistake: In this episode, when Doug and Carrie are taking an adult literature class together, Doug comes down the stairs with his book in his hand, but when he sits on the couch he only has his book pillow and reading lamp, and runs back upstairs to get his book.
Continuity mistake: Just as Doug persuades Deacon to go with him to Carrie's birthday dinner, his position changes completely. (00:10:20)
Continuity mistake: When Sara is in the shower you can see in her shadow, creases from her swimsuit. (00:16:30)
Continuity mistake: The piano in the living room is ebony in the beginning of the episode. At the end of the episode the piano is brown.
Fixer Upper - S1-E12
Continuity mistake: When Spence realises he's eating peanuts, he steps behind the bench he was sitting on, but in the next shot he is in the front of the bench. (00:08:30)
Fixer Upper - S1-E12
Continuity mistake: After Spence suffers from his allergic reaction to peanuts he's seen lying on the couch. Doug then says something to the effect of having to scrape Spence's lunch off the fence, indicating that he threw up. But the allergic reaction took place before they got to the lunch.
Continuity mistake: Arthur and Doug are sitting with beers in the basement. Arthur doesn't open his beer, but the sound of a bottle opening can be heard and suddenly his beer has foam all the way up to the top of the bottle. Arthur stands up and the bottle is still unopened. It cuts to Doug, then back to Arthur with no beer at all. Again it cuts to Doug, then back to Arthur, and he is holding the unopened beer again. (00:18:30)
Fixer Upper - S1-E12
Continuity mistake: Doug finishes playing the tennis game on the TV with Arthur and goes into the kitchen to get the Cheese Doodles. While talking to Carrie, he puts the Cheese Doodle package on the table with a can of cola behind it. He then goes to get a glass from the cupboard and in the next shot you see the cola is in front of the Cheese Doodles. (00:17:30)
Continuity mistake: In the overhead shot when Carrie parks there is no-one around. From the internal shot, there are 2 people visible through the side windows. (00:00:40)
Continuity mistake: When Doug talks about sleeping on his mitt, the way he holds it changes instantly. (00:00:45)
Continuity mistake: When Doug goes to meet up with Ray, Richie zips up his jacket. In the next shot his jacket is unzipped. (00:06:20)
Continuity mistake: The door to the house is on a corner. However, in the interior shots, they have a window each side of the door.
Continuity mistake: When Carrie says that Doug is losing brain cells in the garage due to fumes, the way she holds the tickets changes instantly. (00:12:20)
Suggested correction: Spence did have sex with the teacher, but the episode with the teasing at the poker game, Arthur and the guys don't know about her yet. Therefore, to their knowledge, Spence is a virgin, and for some reason, he decides not to defend himself with the teacher story.
The episode with them playing cards wasn't the only season 1 episode where Spence's virginity had come up. In season 1, episode 12, Carrie fixes Spence up with a coworker. When Richie and Doug tease him that they've already been together a month without sex they say: "Do you believe this guy?" "A month, huh?" Spence replies: "Yes a month! A month is not that long not to have had sex." To which Doug says: "Yeah, but if you add in the other 31 years, I'd think you'd be a little antsy." Also a little later in the conversation, when Doug tries to convince Spence that he and the girl have sex in his garage: "I'm just saying, if you wait too long, this opportunity could go bye-bye. Then it could be, hey, another 31 years before this opportunity comes again. It's pretty tough losing your virginity when you're 62." So Spence later already having lost his virginity in high school is a continuity error that they just overlooked and alas instances like these become apparent pretty often when you rewatch the show (like Carrie becoming an only Child, Arthur being said to be a great piano player in a season 1 episode while he can't play a single tune in a later season etc., etc).