Interesting question. I must admit this is something that I have thought about too. I have always attributed this to my own changing tastes over the years, which is certainly possible. I would say that the vast majority of my "ratings" pretty much have stayed the same over the years. The biggest change in my assessments has probably been to Renee Tenison over the years, who I originally didn't care for at all. It started to change, however, after I saw this video with her and Lisa Matthews on a local TV station in Vegas, I was blown away by her abs and humble personality. I always loved Lisa Matthews, but thought Renee looked much better in this segment, which is amazing, because Renee is the "older" playmate.
https://www.youtube.com/watch?v=HvxozNAwctw
I've also revised my ratings upward over the years for Alana Soares and Karin Taylor, which I suppose shows that I have become more and more attracted over the years to more of the non-white, more exotic-looking Playmates.
The only White Playmate that I've re-assessed over the years in a much more positive manner is Kalin Olson. I think it was the video with Kelly Monaco in the skit when they take off their clothes (of course!) and hang out with their mutual male friend, and jump into the water, and picnic out in nature.
Of course, my ratings for other Playmates have gone down over the years. But I suppose that's a topic for another thread!