Well, whoever said that about new vs reman is simply full of it. Volvo has always and will always sell reman engines and trannies as replacements. They'd cost ALOT more $$$ if NEW. Volvo has had a reman program where their major components are rebuilt for decades. The only time when you'ld get a new engine or trans is when the vehicle is a brand new model (first model year) and there was no available reman parts yet available, otherwise they're always remans.

As for flushing, yes, some mixed DexIII is OK but that's why Volvo wants 16 pints flushed through when doing a synthetic flush. Before all 16 pints are flushed, all the old ATF is gone.

Did flushing you old AT cause its failure then? Doubtfull IMO. Sometimes "stuff" just happens no matter what you do.