So I guess Dan is the only one who can answer this- Is what he teaches, so different that it is a unique thing, or is it that the majority of what Dan teaches is Daito ryu (or whatever system may be applicable) so that his students could pretty easily fit in at another Daito ryu school, or visa versa.
He may very well want to respond to that again, but he kind of did already:
How is it that teachers from Aikido, and Daito ryu as well as Taiji and Win chun tell me I am addressing the heart of their budo?
How can that even be possible.
From this quote: what he teaches is not a specialized "Dan thing," it is generic to these various arts.
From personal experience: the material once worked on
will give you some familiarity with a new martial art. But, being generic rather than specialized, the material still leaves some art-specific learning to be done (like waza), so it wouldn't be considered a complete course in (for instance) Daito ryu.
So the material can be the core of many arts, while not being the entirety of any one art.
Ellis Amdur in HIPS likened the material to the liquid that fills many differently-shaped bottles.