I missed a rollback on Dragster by one car once. We were sitting in the brakes when you could hear everyone yell. Turned around, and sure enough, the train behind us was starting to roll backwards. I was so sad. lol
At this point, they all rely on computers to get it right. They don't do pull throughs, but they do still do envelope tests. Or at least B&M was still doing them a couple years ago. I'd assume they still do. And they have to run so many cycles before they are allowed to put guests on it. But I'm not aware of any coaster company that still manually pulls their cars through a cycle.