to me, shudei just means japanese red clay, but unless someone tells me otherwise, i assume it's from tokoname. many people call 'modern', iron-doped clay shudei also. the fact that we're even asking these questions means we're not all on the same page in terms of understanding and terminology, so i think you increase your chances of being understood by being more descriptive. i'd call natural shudei from tokoname something like hon shudei, but maybe someone else would just interpret that as real/natural red clay from anywhere. maybe tokoname no hon shudei is even better.
i think red mumyoi clay is shudei even though i never really hear it called that.
how is it different than tokoname shudei? not sure. i bet they look different unfired.
hokkaido-dei? hokkaido no shudei?