Presumably any refrigerant that's recovered during a tank emptying process would be stored in a recovery tank containing refrigerant from several other systems. It would in that case, be unwise to try an use the refrigerant in any system due to the possiblity of cross contamination of burn out products, IMO. Others may see it differently. We don't maintain a recovery tank just for the dregs of an empty charging tank.
If YOU want change, YOU have to first change.
If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!