What is the scope of audit variables?

I have an audit variable I am looking to store as a global variable.

I'm not sure how to do this, I have my rule setup as a follows:

$RecordsMissingBP is a global variable.

The script the audit rule executes is:

    $RecordsMissingBP=$Count_Match_BPS;

    print('Legacy IDs found with no matching BP::' || $Count_Match_BPS );

However, this doesn't actually set the global variable as I expect it to. When I check the value later it is empty.

Is the scope of the $RecordsMissingBP limited to not even be the script? I'm not sure why I cannot use this variable in the script it calls.