Specific differences between Eastman and Shires

[Amconk]

I understand that the Eastman branded horns are said to be not compatible with Shires components, but I'm curious if anyone knows specifically what is not compatible? Is it the thread pitch on the bell connectors? The alignment? Is the handslide tenon the same, or tapered differently?

Since the Eastman stuff is "based" on Shires design, what exactly is changed to make them different?

Cheers!