A few years ago, I got a letter from National regarding a crack in the windshield. I searched on FT and some old threads stated that National will send 3-4 letters to previous renters to see who responds. I know when a stone hits the windshield and none did on this rental.
That rental was a o/w from LAX to LGB at a very low price. I called up the phone # in the letter and said nothing hit the windshield. I also stated that I picked up the car after dark. I heard nothing more from them.
When a stone hits the windshield, I will buy a repair "kit" and do the repair. I only had to do that only a few times in the last 30+ years I rented cars. Last year for the first time, I picked up a stone on my personal car and I did the repair on it. There is a small chip but after 5K miles, the chip has not spread after the repair. Before the repair, there was a small "star" with cracks going out from the chip.