Yeah, total crapshoot. I think a lot of it is that there's different aspects to a rod's power but manufacturers only use one general term.
For example, the Common Cents system defines three attributes that comprise a rod's power.
Power
Generally used to describe a rod or blank's stiffness or resistance to bending. See Tip Power, Power Reservoir, Intrinsic Power
Tip Power
A measure of the power of the tip of a rod as defined by the CCS.
Power Reservoir
A measure of the force required to deflect a rod a distance equal to one half of the rod's length.
Intrinsic Power
See ERN. Also expressed in units of grains in accordance with the conversion tables of the Rosetta Stone