Proof white yellowing cant be mitigated?

This pic is from my BB-8, built once, and displayed in a fairly dark room in a fairly deep shelf providing shade. Only window in the room I have put up 3M UV film, and the curtains are closed usually, and its only indirect light anyways. have lots of other lego displayed much longer, and no issues. UCS Snowspeeder, UCS X/A/Y-Wings and more. No yellowing. BB is yellowing like crazy. Wierd part is only some bricks, and not the top ones, some are barley visable yet yellowing like crazy, while...