Acronis update informs me that there is a still more recent build available, however, I did not download it as build 6597, unlike my previous build, does see the 4 backups that I previously created on each of 4 external HDDs.
That being the case, I've created a new backup, and I am at the moment "validating" it. (I've discovered that validating the backup after, rather than during, the creation of the backup seems to be much faster.)
Caution: I haven't yet needed to actually perform a Restore from any of the backups, so I am still not certain that the backups will work.
In a while, I am going to download the latest version of iTunes, and if it mucks up anything (for example, my Playlists or my Star Ratings), then I'll be using the validated Acronis backup to restore the previous version of iTunes and then reporting back later.