I'm not 100% sure what the real question is here as well.
What I do know is that some genealogy software programs (FTM did this in the past but I don't think they do today) use the "XREF" number (in your example I9 or F5) as a person/family ID and think of them as unique values that can be used for merging and database loading.
Unfortunately these numbers are not unique across databases or over time and in the case of the LDS master DB XREFs were intended to be uploaded and used, the XREF is tossed away during the load process. Some people use these XREF values to match people or expect these values to "always stay the same" when loading various genealogy programs. This of course does not always happen, thus my thoughts regarding the REFN tag.
Much like a library catalog number each person should within your database be given a catalog number (not asociated with the XREF) for use in any references to outside databases. I specifically use this catalog number (the REFN tag) as a link to paper documents I have in my library and/or file cabinet and photo database or as original source in paper form. What I mean is that not all of my documents, photos and other information related to an INDIvidual, family or location are housed as OBJEcts in my genealogy database (and for those that are electronic I also keep a paper copy), so I used the REFN number as a catalog number to the file that contain these additional items.