I may have discovered my own answer.
According to an ACI detailing manual, A706-84a has a tensile strength of only 80,000 psi as opposed to the 90,000 of A615-85.
So what do the second numbers, -84a and -85 refer to?
Also, it seems apparent, through research, that A706 IS INDEED "weldable rebar". Will someone please confirm?
Thank you!