DD, hubby does nocturnal home hemo and there have been several times when there has been no way a blunt needle was going in the vein and I have had to open it up with a sharp. He may go months and blunts work fine and then he may have to stick with sharps for a couple of treatments to get it opened up.
Andy made a good point, which I'd never taken into account: the fact that I'm younger (though not young) than the average dialysis patient so of course I'm going to heal more quickly. I don't think that's something I ever saw addressed in all my research on buttonholes.