"ANYTIME" a piece of steel is given a sudden quench from above its critical temperture there are risks involved. "IF" it is not given that sudden quench from above irs critical temperature it will not be hardened. Anyone who tells you otherwise is not dealing off the top of the deck. A 99.99% success ratio means little if your gun just happens to be that .01%. Anyone doing this work should honestly apprise a customer that there is a modicum of risk involved.
Running it through again won't help much if the problem should just happen to be a cracked frame, admittedly a rare occurance, but not totally unheard of either. It would be very interesting to know just what percentage were lost by the original makers on the "First" processing. Every time a piece of steel is Re-Heat Treated the risks grow.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra