Maybe I got into too deep of thinking last night, but something doesn't quite make sense to me...
In "Arthur's Almost Boring Day", Arthur and D.W. are sent to Grandma Thora's house, where she shows them some of the things their dad had from his childhood, including a pair of bell-bottom pants, which he appeared to wear when he was Arthur's age. Now, I believe it was the 1970s that bell bottoms were "all the rage", so considering he was possibly Arthur's age during that time, that would mean that present-day (1996 or 1997, whenever that episode came out), he would have only been in his twenties, which doesn't seem to make sense, because it seems like Arthur and D.W.'s parents are supposed to be at least middle-aged or so.