Old plates

I picked up some old plates, possibly (but unlikely) to be usable.

Whats the H&D scale? And degrees? And the Ilford A-F scale?

Are "ordinary" plates ortho?

Are plates from (I think) the 1940s worth shooting at all?

"Ordinary plates" were blue-sensitive only; ortho and panchromatic plates would be marked as such.

You have lots of questions, but I need a little more information to be able to answer the rest of them. The degrees could be the DIN or Schreiner speed.