As someone alluded to earlier, the freehub bodies have been the same for ages-- the only difference is the smallest cog. An 11T needs and appropriate lockring, and so does a 12T.

A lockring for 12T is too big for an 11T cog and an 11T lockring is too small for a 12T. So long as the lockring size you have matches the small cog, you're good to go.