The back bend was actually the modern technique. At first presses were more strict.
Here is a nice, strict gym press.
Oh yeah, I'm familiar. I tend tend to look look at them from the perspective of:
Pre WWII Strict press which was more or less a Military Press.
Post WWII Strict with relaxed position rules on foot, head, and back bend/position.
Post WWII "Dirty"- Extreme layback.