I do have these registry entries on a system that has ''survived'' both of these updates unscathed. I can also tell you what they are, which you should also know because you have at least one as you say, but on a x64 system you should have a pair as outlined above, one for 64 bit programs, one for WoW64.
On my system, they list the version numbers of the baseline version of ntdll (in my case this is the SP1), the version brought by KB2644615 and the version introduced by KB2872339, the latter also marked as current by this registry key.
edit:
I can also add to this that KB2644615 has also been superseded on Windows 7, but it has been documented as superseded only for Windows Vista. I uninstalled it to test my assumption that it has been superseded, and I can confirm that it has. All this means that I now have only the SP1 baseline version and the newest and current KB2872339 listed. The average user should have many more.