Is anything known about the disposition of the obsoleted recording equipment?  Did it find use anywhere else? 
Were the new cutters installed on existing lathes, or did they also have to update them too?  I'd think that record companies wanting to addrss the ET market would have to update to new dual speed lathes (or were there retorfits?) Did vendor companies make the acoustic cutters, or were they home-brewed at each record company?  At what point did the record companies start to selectively combine microphones and cutters from different vendors?  I assume that the early deals with Western Electric mandated the use of their microphones in the recording systems.   I also assume that when Scully started to deliver their feedback cutters circa 1938, that RCA was the mike manufacturer of choice for state of the art recordings here in the US.