I'm not sure why you say this, there are multiple revisions/versions of the DU out there..sometimes people know what revision they have (maybe on the paperwork?). I think they're at revision O or something now.
Interested. Checked my paperwork, and in Feb 2014 I received a B unit. I BELIEVE that was my last DU replacement (will review the pdfs I have at home as well) and that was about 27k miles ago. So far, so good.