If I understand correctly,
data Int = 1 | 2 | 3 | 4 | ...
All things on the right-hand side are just values.
In the following,
data Maybe b = Nothing
| Just b
Do b in Maybe b and b in Just b mean the same thing? To me, it looks like that b in Maybe b is a type variable, and b in Just b is a value variable of type b.