Shock identity

[SLPreston53]

I got a complete set of "original" shocks when I bought my PU. They are still in a generic box with the only identifying labels being the ones on the frame side of the shock that tells where to locate that particular shock. My question is, how can I tell if these are NOS, rebuilds or those newer ones that do not require shock oil? I am not concerned about NOS/original rebuilt so much as whether I have a set of the non-oil style. Any thoughts?
Thanks in advance!