It is very common for the luff rope to bunch up and "shrink" the luff length. You would have to measure under downhaul loads. Newer sails would then appear to be longer. Depending on the luff rope material used it may have been more prominent at some time over the years. You can not simply lay one on top of another and compare.

We are not talking about H17 sails here, but same applies. Actually more so. Mylar shrinks over time. That combined with the luff rope issue makes comparison difficult.