Need a little help - Datewheel Discoloration

[Cuts33]

So I have been looking to make my first Rolex purchase and would like to get one for my wife at the same time.

She really likes the 36mm Datejust. Ideally I am looking for a nice 16233 ss/yg jubilee with white face.

I have come across several but the one thing I keep noticing is that on some the date looks sort of yellow whereas others it is still a pristine white.

My question is - is this normal? Is it possible the datewheel was replaced on an older model if it has been serviced?

Any help is much appreciated.