Dear Dale,
Thank you for your query.
There is always more than one way to do everything.
I always believed that Revit always places journal files in the journal subdirectory under the main Revit folder containing Revit.exe itself.
You could also search your hard disk for files whose names match the standard Revit journal file naming convention, and even parse their content to verify that they really are Revit journal files, not just by name, but also by content.
However, I assume that using the RecordingJournalFilename property is the only official way to go, and also the safest and most convenient.
You could always store the property value somewhere in the system.
You could also check and compare the property with the stored value every time Revit is started up and issue a warning and/or update your external data if it is modified.
I hope this helps.
Best regards,
Jeremy