Seeking some knowledge on what vintage derailleurs/ what to search for regarding compatible derailleurs Bike is 1982…

Are you looking for the period-correct item? What kind of bike is it, maybe you can search for a catalog and see what was factory stock. Or go to Disraeli Gears and see what was available at the time.

But if you’re replacing or upgrading that one, it would depend on wheel (is that a freewheel or cassette?), dropout spacing, and what shifters you have or would be willing to spend for.