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#31
.....especially older HDDs made at least a decade ago
If they've had it and been using it error free for that long, I don't think that would matter.Count your blessings!
I have only seen the one example. That was a Toshiba 1TB which returned to being healthy, so you can add another brand to the list.
Pending Sector Count are sectors marked as potentially needing reallocation. A SATA drive should reset it to zero if subsequent tests show the sectors to be good. Of course, if they were correctly marked as bad they'll get reallocated, then the yellow flag will move to the Reallocated Sectors Count and the drive should be regarded as unsafe to use.