The one on the left was a bit of an ordeal: the tenon (that I was holding it with while hollowing it out) snapped off. I glued it back on and (after leaving it overnight) had another go and got a bit further and then it snapped off again. I glued it back on again (with some newer glue, in case the old glue was the issue) and had yet another go. That time I managed to get it fully turned and then then the glued-on tenon finally got turned away.
I definitely feel like I'm making progress with this bowling malarkey. Sanding was a lot quicker (especially on the outside surfaces) than the last few and the process is feeling more controlled.