I know the older 2011 solo airs used a valve in the top of the air piston to equalize the pressure between the + and - chambers, where as the newer versions use a small dimple on the inside of the stanchion leg to achieve the equalization. They cannot be interchanged.
The older solo airs were travel adjustable with the use of spacers, the new versions require a whole new air spring in the travel you require.
I think the newer version is better in that is less to go wrong (no extra valve to fail etc), but the trade off is that a new air assembly is quite a lot more expensive than a 10mm piece of plastic if you want to change the travel.
A 2011 Revelation would have their older motion control or black box motion control damper. The newer rct3 damper is a bit better than the older ones. Also, a 2011 RL model for example wouldn't have the shimmed rebound damper. The 2014 Revelation has shimmed rebound on all their models.
Just wanted to point out that there are other differences between that year and 2014 model as well.
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