OK, here's what I think I know:

1. Some substrates aren't inherently tintable, like polycarbonate, and only the scratch coat tints.
2. Therefore, there are tintable (softer?) coatings put on some of these lenses, so you can get a decent tint. Otherwise it's pretty poor tint absorption.
3. Some substrates tint easily, e.g. CR39, 1.6, and I'm guessing no special coating is needed, there.

Questions:

1. What about 1.67 monomers? Does that substrate tint?
2. When it comes to tintable polycarbonate, what options are available? For example, can you order just about any PAL design?
3. Holy moly, what about digital? If you surface the front and the back, I don't know how they even get a SRC!