If anyone is following along, this sounds like something that's easy to do..just extend and measure. The problem is the top out spring. The top out spring keeps the fork from fully extending. If it could fully extend, you would hear, and feel a clunking noise as it hit its extended limit.
The top out spring prevents this clunk, but the fork does not always return to the same point. It's close, probably plus or minus 5mm, but if you are trying to set preload to the exact amount, something more precise is nice, and knowing the fork moves exactly 4.7 inches becomes more important.