Ten days later, on the 25th June, Fox airs a repeat of The Simpsons; appropriately enough, the episode is "Two Cars In Every Garage, Three Eyes On Every Fish". The blackboard joke in the opening sequence is usually "I will not xerox my butt", but for this repeat, a new joke is hastily added: "'potato', not 'potatoe'".
This alternate blackboard -- seen on that repeat, and that repeat only -- has become one of the few pieces of Simpsons miscellany completely lost to time. It's frustrating, because the joke was reported in advance in newspapers, and you'd expect someone to have their VCR switched on for it. I've made more than one attempt to track it down in the past, but as of yet things haven't gone anywhere.
One thing I did think to do, though, was check alt.tv.simpsons for any contemporary posts regarding the joke. Multiple posts describe the blackboard as looking very last-minute, saying that the text visibly shimmered or moved around:
Great bit on the Simpson's tonight....
For those of you who don't watch the show, a running joke in the opening credits involves Bart writing something on the blackboard over and over. Past sentences have included "I will not expose the faculty's ignorance.". Well, though tonight's show was actually a repeat, they did change the sentence on the blackboard. Looked like a last minute thing, since the blackboard portion of the shot shimmered badly.
Tonight's slogan: "Potato" not "Potatoe".