That is exactly my present position. (I'm the cack-handed mechanic, and the new belt is made of Chinesium, whilst the original is made of...er...Japanesium.)
Timing belts, unlike tyres, do not carry date tags, and in an old automobile with little demand for components, they might have been sitting on the shelf for a long period.
Finally, Daihatsu emphasizes in the handbook the need of notfolding belts at severe angles, which is how the replacement belt was kept.
All of this makes me skeptical that I'll be better off post replacement (if I achieve it), but it also makes me much more certain that rubber band autodestructing engines are a bad idea.