They just that tight with info trying to force everyone into buying their over priced belts. It takes people like me that buys, measure, and store the info in order to get around it.
Problems like this is why I now have an upgraded +100" v-belt measuring tool that now handles up to 200" belts. I personally got tire of being sent the wrong length belts and had to prove it to my vendors. I actually threw out one salesman that accused me of lying around the problems. I mean I had him by the shirt collar and put him in his car. I closed that dealer account.
Those dang belts had cost me a lot wasted time and money having to replace the belts that were never the right size. And I still come across their belts and they are still giving problems.