I have pulled film off of cars that have been on there for 6 years before... and it looked brand new. I isntall film so I see it all the time... and have been in business myself for 10 years now. There are numerous films out there and all age differently. But not all of them yellow if properly maintained. The only film out there that should be polished is 3M. It has a topcoat designed for it.... other films do not. I install ventureshield Ultra, Avery Nano Fusion, and Xpel Ultimate and there is no need... in fact not recommend... polishing any of them. By the way the car with the film that was removed was due to it getting keyed on the hood. The person who did it didnt know the film was on the car so they go the film. The car sat in the sun daily but was maintained with Zaino. Looked as good as the day it was installed... I installed it.
I also did some work the other day for a clinet that had 3M installed on their whote Volvo 17 years ago. The film still had not yellowed at all.... I have to say I was SHOCKED. Most film I have seen by 3M that has been instaleld for 6+ years has cracked and yellowed. But this was still in incredible shape. Would have taken a picture of it but I dont install 3M so it wouldnt do me any good.