jnorman, the three essential sound-shaping elements of these vintage microphones are not reproducible any more--their capsules, tubes and output transformers.
What saves the various clone-makers are two main things. One is that many people (even audio professionals) are unfortunately taken in by looks and hype to an embarrassing degree. The company that calls itself "Telefunken USA" has no connection at all with the old Telefunken company in Germany, but if you listen in on the conversations around their AES booth it's as if that didn't matter--they have the authentic label, for God's sake, and in all other respects as well, they've got the look of the microphones down to a T. Unfortunately, enough people with enough money buy into that to make it possible to run a company that way.
The other thing is that the performance and sound quality of the remaining examples varies all over the lot. Manufacturing consistency when these microphones were new was nothing like what can be achieved today. By now these "vintage" microphones are 40, 50, 60 years old, so most have been patched or repaired in various ways. And even if you could assemble one entirely from original, unused parts from your grandfather's storage locker, it wouldn't sound like it did back then because the materials change with time as well as use.
As a result, every aficionado can pick out his own favorite U 47 or M 49 or Ela M 251 (etc.) and claim that this, indeed, is the true U 47 or M 49 or Ela M 251 (etc.) sound. And no one can really contradict him--not even the original manufacturers, since their own vault copies of these microphones also varied in the first place, and have aged as much as the rest of the flock. But I guarantee you that (for example) Klaus Heyne's concept of how a U 47 or a U 67 ought to sound is different from (for example) the late Stephen Paul's idea and from (for example) Tracy Korby's or (for example) anyone else who owns or works on these microphones. There's room for all these opinions; none are wrong. It's "whatever the market will bear"--a universe of rubber yardsticks and clocks that melt. Everyone gets what he wants until the money runs out, like in "Mahagonny."
--best regards