Yes staingate can change for free. As long as within 4 years of date of purchase. Anyway, replacing new screens doesn't mean it won't happen on future screens. I kinda hope they fixed it on 2016 MBP already.

Yup, but to be safe best replace within 4 years of purchase. I have a little bit of staingate but I am in no hurry since new screens don't guarantee the problems will go away.

Btw, I hope its got nothing to do with ur new 2016 MBP...

I have read somewhere that the staingate issue is partly cause by the heat radiating out so nowadays I have been extending my screen all the way back except for video conferencing. However no idea is true or false...but I have been wiping the screen with a slightly damp cloth instead of a dry cloth and haven't seen any new stains appearing...