Modify > Split > Split Selected Members at Nodes allows you to split selected members at nodes which are located on but are not connected to these members.
The following figure shows a shell with edge members on four sides:
The following figure shows shells generated by sub-meshing (2x2) the shell from above:
Notice in the figure above, the middle nodes on the edge are on but not yet connected to the members.
The following figure shows members generated by splitting members at nodes.
The figures are rendered using the command View > Render, with the rendering ratio of 80% for both members and shells.