TortoiseSVN and TortoiseGit both use the same nine icons, Dropbox uses eight, and if you have OneDrive installed (which you will if you use Windows 8 or above) then it uses three. And Windows itself uses a few to indicate offline files or enhanced storage. That’s 22 icon overlays.
The problem is that each of these applications uses multiple overlay icons but Windows only uses the first 15.
The icon overlays can be found in the following key:
It turns out you can safely rename the folders which will reorder the icons.
Attempt to stop applications from changing the order (this is likely to cause problems when adding a new program that uses overlays):
Can also try to use ShellExView to disable unused Icon Overlay Handlers.
Annoyingly both Dropbox and OneDrive have also resorted adding spaces in front of their names to exploit this, instead of getting microsoft to fix the 15 limit.