If Command Extensions are enabled, then there are several dynamic environment variables that can be expanded but which don't ...

If Command Extensions are enabled, then there are several dynamic
environment variables that can be expanded but which don't show up in
the list of variables displayed by SET.  These variable values are
computed dynamically each time the value of the variable is expanded.
If the user explicitly defines a variable with one of these names, then
that definition will override the dynamic one described below:

%%CD%% - expands to the current directory string.

%%DATE%% - expands to current date using same format as DATE command.

%%TIME%% - expands to current time using same format as TIME command.

%%RANDOM%% - expands to a random decimal number between 0 and 32767.

%%ERRORLEVEL%% - expands to the current ERRORLEVEL value

%%CMDEXTVERSION%% - expands to the current Command Processor Extensions
    version number.

%%CMDCMDLINE%% - expands to the original command line that invoked the
    Command Processor.

%%HIGHESTNUMANODENUMBER%% - expands to the highest NUMA node number
    on this machine.