Good question- and my answer is "pretty much, yes" Difference between III and IIIA is the jump from 357 Mag to 44 Mag- and to 9mm at subgun velocity. Problem is not resisting penetration, but rather what to do with all that energy that was driving the bullet? Cannot recall seeing a IIIA that did NOT have the trauma plate to spread out the energy. Otherwise, vest stopped the bullet, but being hit in chest by sledgehammer stopped your heart.
And BTW- ain't NOTHING bulletPROOF. It is bullet resistant.