Defensive Weapon Training states:
“The fighter gains a +1 shield bonus to his Armor Class. The fighter adds half his weapon’s enhancement bonus (if any) to this shield bonus.”
Defending melee weapon quality states:
“A defending weapon allows the wielder to transfer some or all of the weapon’s enhancement bonus to his AC as a bonus that stacks with all others.”
If I understand Defensive Weapon Training correctly, a fighter that applies this Advanced Weapon Training feature to a weapon group he possesses — in this case, heavy blades — gains a shield bonus despite not actually using (or even holding) a shield. If that same fighter was wielding a +2 longsword, his shield bonus would be +2.
What if that same fighter was wielding a +2 Defending longsword? Would he be able to utilize a +2 shield bonus (courtesy of Defensive Weapon Training) and a +2 bonus to his AC (courtesy of the Defending melee weapon quality)?
Essentially, can RAW allow you to use one enhancement bonus twice, at the same time?
No.
And the key here is the words "if any"
You've transferred some of your enhancement bonus. It isnt there. It doesnt get a +2 to attack. Or damage. Therefore it cant be used as a secondary pool to double dip.
Once you've used that pool to boost AC, you can't then use it a second time.
Mathematically you could gain a bit of bonus transferring some out and still having an even number left to cut in half to boost ac. But you can't double dip.
I see no way RAW allows this.
Thank you, Cavall!