Jeff you were a 6.5 when you shot a 71 (-.8 differential). Yes, it can happen. Once in 1,200 rounds according to the USGA. Or once every 21 years according to your GHIN playing 57 times this year. Your GHIN dropped to a 4.9. It went down 25% on your own index from ONE score.
In an event of your peers, playing to an ability that will drop your own index 25% is one of the main reasons we even have an adjustment formula in the first place. I don’t need a computer to tell me your index was about go down. That’s what our adjustment formula does. Proactively revises just like your own GHIN will.
A 4 index established at the hardest course on the planet and a 4 index established from Mickey Mouse CC are identical in ability. They are no different. You playing from a shorter yardage is a mere opinion as to why you play better here. The differentials (ability course to course) are likely similar. Gross score is the only thing that changes.
Never going to say it’s a perfect system but to say that instance didn’t warrant an adjustment I couldn’t disagree more with.