One more thought: Indexes for holes are reckoned from the back tees, and there are MANY cases where the hole changes dramatically as you move up OR change the angle of the tee shot.
Is that really how it should be though? Most people don't play from the tips, so calculating the indexes from there doesn't make a lot of sense to me. The whole point of handicapping is to help level the playing field between golfers of different skill levels, but if you have golfers of different skill levels playing against each other, unless it is a very short course they are unlikely to be playing from the tips. Otherwise you risk handing a huge advantage to the longer hitters, at least on courses where the back tees have forced carries just to reach the fairway.
Are any GCA events played from the tips? I doubt it, unless it was held on a golden age course that was last lengthened in 1927.