The only placeholders you need to keep in mind are those used in the MasterIconList.txt file, that is, the overall icon assignment list. Any shp file or icon out of these bonds will not be considered by the game.
Read this file thoroughly, you will find the holes in the actual list and the unused/ uncreated files counted in the list. Once again, these are the only ones the game will look at.
As far as I know SHPed doesn't allow to create shp files from scratch, so the best way to create a brand new file is to edit any original file containing few icons. The icon shp in the game are generally filed up with blank images, so you can use one of these. Reversely you can use any file and replace any unneeded old icon with a blank image (full background color).
To add a new icon at the end of your file use (carefully) the last top-right button in the main window, while making sure the number entered is
always that of the last existing image in your file. else bug
Hoping I have answered the right question this time!
Otherwise I guess you can post here again. And again... and again
