In the episode where the carines take the house, Homer goes to the door to ask about the ring-toss proposistion. Then the door has a peep hole. Later when the Cooters are saying they were beat by the best, there is no peep hole! WHOOPS!
I just built a Gingerbread Simpsons house, and spent months researching it. A lot of the little things like mailslot & Mailbox, peepholes, etc. are just plot devices for a particular show. This is nothing, how about Maggie & Lisa's switching rooms, or the seldom seen rumpus room, or the two mystery rooms over the garage?