I realize that i didn't really address the original point (Roblowe14)
two different implied questions:
a) will the newer Revisions work in an older switch
b) will the newer Revisions connect to the older xcvr on the other end
YES, the technology of a Rev C or Rev D (or even Rev E) are the same.
The newer Rev Xcvr will optically connect to an older xcvr of the same type; J4858C over fiber will work with a J4858D.
Thanks Davide for watching out for this topic.