Hi Fraser,
The first two tokens that you list in your example ([CUR_USER],[CUR_NT_USER]) are old tokens that are still supported for backwards compatibility. These are the equivalent of [SYS:CUR_LOGIN], which can be used instead.
The other items you list ([STEP],[HOLD], etc.) are special values that are not parsed by the token parsers. Instead, these are specific to the activity types they are used in, and are just substituted by the Workflow Manager application. These are not supported in other cases beyond the out of the box activity types.
The list of documented tokens is the complete list of supported tokens that can be utilized in any aspect of Workflow Manager that supports tokens.