All three were purchased over the last 4 months or so - possible they are from the same batch I suppose. If I look at the underside of the bars, the etched lines hit the two cutouts in the sleeve in different places, while the cutouts seem to be centered. This seems to indicate that the lines were just etched a little bit off, with the bars being ok otherwise. Certainly the old Schwinn stem isn't perfectly symmetrical either.

I think I will just center it on the lines - can't imagine it will make any difference riding and at least it won't look wonky. I love Nitto's bars and stems, so was surprised to see this kind of lack of attention to detail!