Quoted from pinballholder:johnwartjr posted a few years back "I've been told 200 Whirlwinds and 100 Rollergames had Diamondplate. As many of each as I've seen, I'd suggest the figure was more like 1000 Rollergames and maybe 500 Whirlwinds."
So best case, about 20% had DP.
DP rollergames are sample games. I think they should have kept the chrome wireforms and urethane topcoat for all 5000 pins.