Analyzing a line of the Scotch Four Knights made me realize just how much undiscovered territory there is as long as you go far enough back in history. The reference sources I used were all as bad as each other, probably because authors’ views had been copied without checking things with a GM/chess engine partnership.
This reminds me of a remark of Bent Larsen to the effect that it was easy to be an expert in ancient openings. So let’s hear it for things like the Four Knights, King’s Gambit and …. the Vienna: