I've had the car for just about the last 100,000 miles and did not change the belt since I have had it. Heaven alone knows what kind of belt it was. The lettering on it had long ago worn off, and the back side of the belt was nothing but a network of cracks that went all the way through the rubber to and through the teeth. Come to think of it, the front, or toothed side looked like that too. Literally the only thing holding it together were the cords in the belt. I should have taken photos of the old belt and posted them. It may still be somewhere where I can find it. If it is, it is possible that I'll post some photos.

Normally I am much better at maintenance, and would have changed it long ago. I certainly don't recommend that you try to get 100,000 miles from your new belt. Not even 75,000. Change it in accordance with the recommendations in the user manual, or the Brickboard FAQ, or an average of the two if they differ. That your belt was still in good shape is the whole point of the change interval. It is like cleaning, vacuuming, and dusting your house: You do it regularly, even if it does not look like it needs it. It is much easier that way. You certainly don't wait until it is covered in a foot of dust and there is schmootz all over your carpets.
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1955 Human, Scott; 1991 745 Turbo, Thunderbolt; 1990 745GL, Posideon