I think with trail rating it has to do ground clearance, sidewall depth, approach and departure angles, articulation. They are different ratings with in a trail rated jeep. for example the Wrangler has a much more severe rating. I am sure it could also involve axle housing strength, torsional rigidity of the chassis. I think in a rubicon has underarmor added as part of the package as well as tow hooks. Jeep doesn't really give much information about how they trail rate becuase they want to keep their competitors in the dark.
When you get knee-deep in a situation, floor it.