@Mike53
I'm not sure what sort of pictures or description you expect...
Why some groups share "sweethome3d_opening_on_hinge_1_" and differ in last phrase? That's because all of them are supposed to rotate around the same hinge at the same time but each one has different material aplied (they can't make one group)
"Sweethome3d_window_pane_on_hinge_1" is special prefix - combination of "sweethome3d_window_pane" and "sweethome3d_opening_on_hinge_1"
Why hinges with the same color are not in one group? Because they are not connected and probably would be exported as separate groups anyway - it depends on modeling software you use. They could make one group as well.
Hinges (visible or hidden) should be centered on axis of rotation parallel to height, width or depth of your model (assuming it's oriented properly to axes X,Y and Z). The largest dimension of all selcted/grouped objects making one hinge should be oriented along that axis/dimension.
