in the golden freddy's Maintenance Section when you are cleaning golden freddy's suit and pulling out the bodies;in the right up corner we can see that parts of other animatronics(including:freddy,bonnie,foxy and chica) getting removed of your inventory so we can safely say that we used those parts to kinda upgrade golden freddy's body like how we replaced the purple hat and bowtie with black ones.

when the kids died they haunted the animatronics and if we added some parts of those animatronics to golden freddy there is a chance that the entire MCI (suzie,fritz,gabriel,jremmy and cassidy) to haunt golden freddy alongside with dave and cassidy

BUT HEY THAT'S JUST A THOERY A FNAAAAAF THEORY