Just my thoughts...
With regard to how much time Paul or James work on each other's cues, I don't think it really matters, as has been stated. It is a matter of quality and workmanship. What I find interesting is that when James broke out and started selling cues with his name on them, he immediately got virtually the same price that Paul had been getting. I thought that kind of strange. The only "apprentices" that seemed to be able to do that, as far as I know, are Pete Tascarella and Barry Szamboti. Any others out there that I forgot?
Other apprentices seem to have had to start out pricing their cues more reasonably at first to get their name out. Some still don't get the money that their teachers are getting, such as Mike Wheeler. He has worked in Richard Black's shop, and has been with Schick for quite a while, but his cues don't get half the same money. They are virtually the same structurally as Bill's, and hit the same.