You only need to change the RT_version property in an RTR file whenever the contents of the RTR file change. Choose a value for this property that clearly indicates that this version of the resource type is the latest version.
Do not include the following characters in the RT_version string in the RTR file or registration of the resource type fails:
Space
Tab
Slash (/)
Backslash (\)
Asterisk (*)
Question mark (?)
Comma (,)
Semicolon (;)
Left square bracket ([)
Right square bracket (])
The RT_version property is required.