As I read your question..
..yes, it's hogwash...nonsense, even! The '13' being the taper º, being equated to a 'C'. Those are 1'34" taper, or more commonly referred to as 1-1/2º .
For reasons I've never understood, the 'number' of tapers is often called one more than it really is. A KTM needle (NOZH for example) has TWO different taper angles, but I've often heard them called 'triple tapers'. Maybe the people that call them triples are including the L1 in the count?
He's right in the 'proprietary' part as far as direct crosses to keihin parts. As you've seen, sometimes the numbers don't match up perfectly.
Are you aware of JDs tuning guide? You can graph mulitple needles for diameter to throttle axis, and fuel flow to throttle as well. Good for doing exactly what you're looking at..the changes brought about in different throttle positions with different needles.