The supposed 1964.5 was a 1965 it was just released midway through 1964.
When Ford released their next model year midway through the current year they got the jump on everyone.
Since then it has become commonplace to release the next model year vehicles midway through the current year.
There are no 1964 1/2 Mustangs. They are 1965's that were released mid year.
So it is, in fact, the 2015 Mustang IS the 50th anniversary Stang.
Happy Birthday to the Mustang!
2013 V6 Convertible
Eibach Anti-Sway Kit, FRPP Foose Stallion Springs, Koni STR.T
2013 Grabber Blue GT