It seems to be extremely common to believe in disks that use the spinning-down platter to drive the motor as a generator to power a last few sectors' writes. When I speak to engineers at drive manufacturers, they say it's a myth. (It might have been done decades ago.) They say they happily stop writing halfway in the middle of a sector, and respond to power drop only by parking the head.
Some drives only report blocks written to the platter after they really have been, but that's bad for benchmarks, so most drives fake it, particularly when they detect benchmark-like behavior. Everyone serious about reliability uses battery backup, so whoever's left isn't serious, and (they reason) deserve what they get, because they're not paying. Building in better reliability manifestly doesn't improve sales or margins.
If you pay twice as much for a drive, you might get better behavior. Or you might only pay more.
If you provide a few seconds' battery backup for the drive but not the host, then the blocks in the buffer that the drive said were on the disk get a chance to actually get there.