Fright Night - S4-E6
Plot hole: After the girls get their revenge on the boys in the attic, they explain the mysterious "I must have air" voice from the trunk as it's revealed to be from a tape recorder. Marcia mentions a set up the girls had where they played the tape recording (from their bedroom) when they were ready. This is impossible as the recorder was in the attic trunk and the play button would have had to be manually pushed down by an actual person to activate.
Career Fever - S4-E9
Plot hole: Peter thinks he has a fatal disease. The parents realise two pages stuck together and he went from page 95 to 98 mistakenly. However, Mike first read about the actual fatal disease info on page 97, and then Carol read about what Peter actually had on page 96 (poison ivy). If Peter read only 95 and 98, there would be no way of Peter to know his disease was fatal since that was printed on page 97.
How to Succeed in Business? - S4-E19
Plot hole: At one point Peter admits to Greg he was fired. In a later scene, Peter tries to talk the parents out of going to the bike shop (where they think Peter still works), and soon after the parents ride new bikes and see Peter in the park and admit to him that his boss told them what happened. Carol said that Greg filled them in as well. This is incorrect because before leaving the house, they didn't know of the firing, and went straight from the bike shop to the park. Greg never told them.
Suggested correction: Just because we didn't see it on camera doesn't mean it didn't happen, it's known as "implied action."
That's not really the case here... the sequence of events explain it all. It went from going to the bike shop to find out what happened to the park. Even if they went home in-between, there would still not be a reason to have to question Greg, since they know what has happened at this point.
To build on the implied action point that the user stated, we do not know what happened off-screen so it's not impossible to believe that Mike and Carol went home after learning about what happened from the boss to talk to Peter and then have Greg explain where he may be and why. Peter did tell Greg about feeding the pigeons in the park so it tracks.