I picked up my model 3 in Dec of 2018 and took it to get tinted all around (including the glass roof) with 3M Crystalline tint within about a week of picking it up. I still have it, and have not had any problems with the windows being tinted, including the back window in 1 piece.
I took my wifes 2022 Model Y, purchased in March of 2022, to be tinted at the same place, with the same tint, 3 days after picking it up. Its been a little over a year, and no issues.
I wouldnt have done half tint on back window on either of them, as I cant stand how that looks in the car. I would have either done what I did ( full tint, 1 piece) or not tinted them at all. I was told that a lot of shops dont carry the tint roll size needed for the large back windows of model 3s back when I did mine, not sure if thats still the case or not.