So if the conductors are not loaded to their maximum load capacity then I do not have to derate?
No, you must derate.
Could you put a 12 AWG on a 30 amp breaker as long as you only load it to 20 amps?(forget about 430 & 440 for now
Derating is just what it says, the conductor is no longer rated X it now rated less than X.
While what has been said does make sense and I agree it will work IMO it does not meet the code.
I also do not think you will sell this to an inspector.
Apparently there is no definition of load diversity from the NFPA.
When you have a derating table that is based on this undefined load diversity that means they already based the table on mixed loading.
If all the conductors where for some reason fully loaded this table may not provide enough
Derating table 310-15(b)(2)(a) is no longer based on load diversity. In the 99 code there is an FPN directing you to Table B-310-11 in the rear of the book which is a derating table based on load diversity.
It does not eliminate derating it just eases it up a little.
How do you convince an inspector that you can use Table B-310-11?
I have no idea, FPNs are not code.
IMO the only chance you might have is if you have a electrical engineer sign off on it.