Thanks. I agree that there are workarounds, and I do have multiple other protections in effect already.
Yes, sure one could create entirely separate backups for these particular files, and then have a full exclude for them that affected all drive level file backups (Full/Diff/Incr).
But one should not have to. :-)
Since, when it comes to backups, I by long experience have learned to wear all of Belt, Suspenders, and at least two thick strings to keep my pants up, I also separately run Macrium image backups of drives.
In addition to constant file-history tracking (which excludes PST files) and separate file-sync copies of important files spread around onto both other drives and my Linux file server. I do not trust any single piece of software (not Macrium either) or hardware to be enough to protect me, so I have multiple types of software backing things up to multiple locations in multiple formats. Protecting me from inevitably failing hardware as well as from software that might fail to work as intended when you ask it to restore. :-)
Plus, all drives are running RAID 1 (mirrored), protecting me from all the usual single drive failures. This has so far mostly protected me from ever actually needing to roll in a full backup of anything.
So, yes, if rooting around in all my many backups/copies in case of a (multiple-)disk crash, I surely can find those particular files, to restore them separately, after restoring what SHOULD otherwise be the only necessary backup (roll in from a full, then Diff/Incr).
But again, one really should not have to do all this "keeping track of individual files" in what should
be a complete disk backup, since each type of backup should have a sequence of Full/Diff/Incr that combined should be enough to accomplish a restore. Without having to remember and track separately that certain individual files should be found elsewhere, because the software making that particular backup is limited. Hence my request to be able to add separate "excludes" to Diff/Incr backups.
I really want my "excludes" on full backups to be only dumb stuff like temp and other junk folders.