They were not covered because, frankly, they are not nessicary. You can cram a lot of gamming into the first 20 levels, and the power curve is sufficent to model anything from wet-behind-the-ears novices to Conan himself at the height of his power.
Now, that doesn't mean that it's wrong to want to game beyond level 20. There is no such thing as wrong so long as you and your group are having fun.
However, building a system that works equally well at level 2 and level 52 poses some unique, and significant, problems. Both for mechanics design and for world design. So, from a game designer's perspective, why spend time and effort trying to break down those obstacles when the results are not nessicary to the final product and would only serve a small sub-set of your audience in any case?
And that is why they don't address "epic" rules in Conan.
Later.