Front windshield usually we took off. Front passenger depends if visible 50%, then we jz ignore.
As you said permitted percentage, do u calculate uv of the glass + tinted percentage? Even your tinted is qualify but not all glass suitable to pass. Example bmw, uv glass + 50% tinted on front passenger. At puspakom will fail, bcz on their device passes usually are 43-44%. You can try yrself by drive a tinted car to puspakom then you will know d result. I jz share my experience.
Yes, when u sell yr car, u can transfer yr number plate to new ap. (Usually u can buy a new ap from motorcycle shop, they will charge u around 1k).
So when u buy new vehicles, u can transfer the new registration number to the old ap u have.
Hope u can get a clear picture.
Only new number plat can exchange with 2nd plate.
Buying 2nd plate (exp: WW1) cant direct transfer to current number plate. If u buying new car (come with new plate) then you can buy a 2nd plat (exp: WW1) to exchange with current plate (exp: WC 7306 S)