I have three black backpacks that look exactly like this one. They are all White Stag.
I also have one orange that was sold by Nemrod.
In Puerto Rico (at Divers Service Center, in early 1970's) we used to import some gear that wasn’t as common on the rest of the US and I remember seeing these packs being sold by Nemrod. I did not see the White Stags until later. I think they look like they came out of the same mold (or very similar).
An important feature of this packs is that the plastic is a lot more flexible than the one used by US Divers in their contour packs. The US Divers packs were very brittle and would crack very easily.
Just gently laying the tank down on top of the pack would easily crack it. The weight of the tank was enough to crack the pack at the bottom.
These packs on the other hand are much more flexible and forgiving to abuse. They will flex and bounce back without cracking.
I often use all three of my black ones for pool sessions when I am sharing a double hose kit with any of the local dive club members. On this events the backpacks get a lot of abuse, and they still work just fine.
These are also extremely comfortable backpacks.