It's well-established that Narciso Yepes, in close collaboration with Jose Ramirez III, came up with the design and specific tuning scheme for the modern 10-string guitar. This all happened around 1961 to 1964, no one seems to know the precise date of the 10-string debut. Even the location of that concert (Madrid, Barcelona, or Berlin) is up for dispute. And again, I am specifically referencing the modern version, and not factoring in Carulli's decacorde and/or other 19th century designs. But what about the modern 8-string? The earliest one I can think of (again speaking of the modern design) was Jose Tomas's Ramirez, built in the late 1960s or early 1970s. Was this designed as a "smaller/simpler 10-string"? And what was the initial "preferred" tuning scheme for the 7th and 8th strings? On my own 8-strings, I've tended toward 7=B and 8=D, a re-entrant sort of tuning, and this is meant for renaissance lute music*. Drew Henderson uses 8=A and 7=D. Paul Galbraith and others throw a real curve ball here, by keeping the "main six" strings in slots 2 to 7, and adding a higher and lower A string to the outermost slots.