every tilepart has voxel data (12 double-layered loftemps, defined in an MCD file) unless, uh it doesn't (blank loftemps)
I don't believe there is any loft-data implicit in the engine ...
loft-data for walls, etc might not be what you'd expect; you should use MCDEdit or McdView to see the lofts used for a given tilepart