For a junction reparse point, Sysinternals junction.exe shows the "Print Name" and "Substitute Name" are the same and it's not an NT \?? path (i.e. \DosDevices, i.e. \Global??). OTOH, the substitute name does use an NT DosDevices path when I use cmd's mklink or os.symlink to create a directory symbolic link to an absolute path. 

I modified the patch in a test program to see whether it's really necessary to include the DosDevices path in the substitute name. FYI, it seems to work fine without it, but it also doesn't seem to hurt to include it.

Sysinternals Junction
http://technet.microsoft.com/en-us/sysinternals/bb896768.aspx