Eames 'Eiffel' base authentication?  

Vintage Eiffel (US)
Eiffel bases with the first generation glides are pretty hard to come by. The rubber/metal or off-white nylon glides are more typical. Vintage Eiffel bases are zinc(?)-plated or black (not chrome). The vintage Eiffel bases have thinner rods than Modernica or current Vitra production.
Other than Modernica, I've not seen other reproduction bases up close so I can't really comment on specific differences in those.

Said bases in question
Here are few images of the chairs / bases I'm specifically talking about. Yes, I know the last base is a bit bent out of shape...

Hmmm
Difficult to say with certainty. The glides certainly appear to be vintage with discoloring over time. Bent rods are a common occurrence with used, vintage bases. Judging from the photos, the black finish looks a bit shinier than the ones that I've seen. It's possible that these are just in better shape.
Measuring the rod diameters may provide the most definitive answer. The rods do look to be a bit thicker than vintage Herman Miller (difficult to tell for certain from photos, obviously).

Reproductions
These bases are from modernconscience, 100% sure.

I have sold these and also a...
I have sold these and also a lot of original bases. Differences in the top anchorages, finish black wires and compounds (where two wire ends are welded together) in center section base.

@joink
Could you be slightly more specific on exactly what the differences are? If you could point to any pictures that show these differences it would be greatly appreciated. I'm not too familiar with the 'Eiffel' base, so please forgive me.

Please see attached picture...
Please see attached picture for some details.
You can also mail me with questions.

@joink thank you very much
You couldn't have made it more clear. That's perfect.