When Eric and Donna are at Mount Hump, they sit down and talk. As the van starts to roll and passes behind them, the whole set shakes and Eric and Donna move sideways a little bit.
When Kelso is date-stamping the books, he doesn't change the stamp to make a different date.
Eric and Donna go to Mount Hump where they can see several mountain ranges in the distance. The show is set in Wisconsin. Wisconsin has no place where there are several mountain ranges can be seen like this. The highest point is Timm's Hill elevation 1951 ft.