The "B" lifters (18538-99B) were used in the 2007 through 2010 model years, then Harley went to the "C" revision level sometime in 2010. The problems seemed to get worse with the "C" lifters, but that isn't to say that there were no failures earlier, there were. The "C" lifters also had many more issues with the hydraulics, not just the rollers. Complaints about leaking down and being slow to pump back up really increased with the "C" version.
The root cause, IMHO, of the roller failures has more to do with the rest of the valve train. Harley put a cam in the 110's that has very abrupt ramps, heavy valves, and then compounded the issue with very high pressure valve springs. The combination put more stress on the lifters than previous designs, and obviously the lifters weren't up to the challenge. I can't remember hearing of this roller issue on the "B" lifters in earlier engines with less radical valve trains, and even the "C" lifters haven't had a major failure history in the non-CVO engines. Harley still uses the "C" lifters in everything but the CVO110.
Btw, I think the "C" stands for Cheap Crap, but of course I could be mistaken.

Jerry