There seems to be a copy & past error in [mdspan.sub.map.right.1.3]
otherwise, submdspan_mapping_result{layout_left::mapping(sub_ext), offset},
I am pretty sure this should read
otherwise, submdspan_mapping_result{layout_right::mapping(sub_ext), offset},
Also there is some misformatting in https://eel.is/c++draft/mdspan.sub#map.right-note-1