1969 Topps baseball backs
 

I am sorting through a few 1969 Topps baseball sets and notice that the backs can be either (1)a vibrant white and pink or (2) a dull off white and salmon. I used to think they all started with the same vibrant back and the off white backs resulted from age, heat exposure, or other environmental factors but now I am not so sure. I have many "used" G-VG cards with vibrant backs and many near mint cards with off white backs. The off white backs seem to outnumber the vibrant backs by about 5:1.

Are the cards printed on two different stocks? Can anyone shed light on this?
Has anyone opened a wax pack or vending box recently and noticed the condition or color of the backs?

I think Topps routinely used two different stocks, one that stays white even 50-60-70 years later and one that tones. Not sure if the better stock was early print runs, raks, etc or just random.

Yes, either two different stocks, or they had a layer of white under the rest of the back.

I haven't had enough of them to tell if either is anything special, or if it's more common on certain series.

The same thing was done in other years as well