In my experience, Dips, PullUps, and most DB exercises do not progress with the same predictability and consistency that barbells do. When I program these exercises for clients, we always work within a rep range. 4-6, 6-8, 8-10. Etc. I'll usually progress them when the majority of their sets are hitting the upper limits of the range. But I don't wait until all the reps are. So if I programmed 4x6-8 on Dips, I'd progress when the client go 2x8 with the given weight and the other two were at least 6. Make sense?