Help with Jaeger Lecoultre Master Movement

[rickc007]

I'm looking to buy a JLC Master Control Date
and noticed that the rotor through the see thru back is different on some.

Not sure how to tell which is which, because all listings have the same reference number Q1548420

The early version did not have a see thru back.
Below are the two different versions. One has a silver rotor, the other gold.

Anyone know how to differeniate the two, or any pertinent changes in the model in past years ?

Thanks

[Justindo]

The gold version is the newer version and is at least a couple years old. It looks better to me, but either should function identically.