I know I've said this before, but I reiterate that I think we're looking at some sort of coordinate system here. Given that the alphabet has its origin in shorthand, and coordinate systems of notation are a standard feature of shorthand systems, I do not find this too unlikely. Systems ranged in coordinate notation up to 12 points of the compass, so a simple system of four compass points 50-80 years before the publication of the first coordinate system is not out of range. Variations on a coordinate theme were also covered by Porta in 1568, and I'll have to check but I think the idea came up even earlier.