As far as lumber grading, unless I visit a sawmill the traditional lumber grading doesn't seem very consistent or accurate. I attribute much of that to the scarcity of large trees, as much of the available timber land has been cut over two or more times and trees never get more than 18" in diameter. I have not seen "cabin grade", but would view it as suitable for a woodshed until proven otherwise. Corporate speak for sell them what you have, even if it's garbage.
The choke designations bother me as well, but I simply won't buy a choke marked in other than a traditional way. That leaves three options for marking:
1. Full, LFull, IMod, Mod, etc.
2. Constrictions, i.e., .040, .035, .030 etc. These do require knowledge of the bore diameter to make any sense of.
3. Euro designations, i.e. 1/4, 1/2, 3/4 etc. In a 12 that would be roughly IC, M, IM/LF
Aside from the dumbed down designations, I won't use an extended choke either, except for turkeys. The reason is weight at the muzzle. If you want to test it for yourself, take a flush mount and an extended choke of the same constriction and material. Swap them out, swing the gun a few times with each. You will feel the difference, especially in a double barreled gun. I like a lively gun, if you enjoy a pig on a shovel the extended choke is for you.