Okay.
So, I had seven files for which data - that was meant for {File.MD.XMP::dc\title\Title\0} - was instead incorrectly deposited into {File.MD.XMP::dc\description\Description\0}.
The MD Mechanic worked great. Filling the Title tag - via the Set to operation - with what was already in the Description tag.
What was just a tad strange, however, was after I did the metadata write-back for these seven files: The Title tag now had the data, which is what I wanted. But, the Description tag was now empty too, which is also what I really wanted.
But, I was under the impression that I would have to first manually delete the Description tags myself for them to be clear. But, instead, the write-back effected this. Is this normal, or is this a glitch?
The MDM only modifies the tags you use.
When I copy the description to the title the description remains untouched (same values for both title and description afterwards). Writing back also does not change the description.
Check the description tag content on your system after running the MDA. Is the tag empty?