Yesterday I had to add some extra drawings to an existing job by putting extra layouts in the middle of some existing ones in one dwg.
Once you have added the new layouts to the drawing and Sheetset Manager (SSM).You can not just start renumbering drawings in SSM.
Say for example you have the layouts numbered 200,201,202,203 and then copy 201 and make a new layout so you have 200,201,201(1),202,203. If you go to SSM and renumber 201(1) to 202 things start to go to custard in SSM as a layout 202 already exists in the drawing.
To add a new 201 drawing to SSM and have everything in sync you have to renumber 203 to 204 , 202 to 203 and 201 and then renumber the layout 201(1) to 202.
Someone may know of the correct way of doing this but this is how I worked around it for now.