My problematic-file indexing is back to working again. Not sure why. (I checked much earlier today after indexing had been well completed... and the error was still there. Sigh.)
Thank you very much @Vero for highlighting how I overlooked the "here's how to tell if re-indexing is done"... my fault for not seeing that earlier, apologies. I still want the means to re-test previous version of Alfred by downloading them, now and any time in the future. Is Alfred refusing to provide this? (It's okay if Alfred will not provide this. I'm simply seeking a definitive "yes we will" or "no we will not" answer. I'm not trying to be mean or difficult.)
I did _not_ save my 'Built-in Troubleshooting' (I do not know what the URL anchor is for that section) error output from earlier... that was a bad move on my part, again my apologies.
Doubtful it's a scope problem, but never say never. The scope had not changed from "working" to "not working"... and the indexing was finding the similarly-named files in the same directory area (specially: dated-snapshot-backup copies were found in a subdir of the problematic could-not-find file location).
If this happens again I'll be smart and post all my data here (and get over the fact I'll have to spend time redacting the info).
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All in all... I've just plain grown tired of what are simple file-indexing problems for macOS/Spotlight/Alfred over the years. I'm not sure who/what is at fault. But it's a mess and it's one of the few things on my computer that feels like the computer is "just being emotional and there's nothing deterministically I can do to fix/solve it"... and I've just grown tired+emotional myself of this topic. Given all the docs Alfred has written on this, I suspect it's a drain on them, too.
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