Launderess:
From what I understand, before the KDS-19, none of the machines did any thermal holds or any significant heating during the washing phase (Main-wash).
They did use a 700w heater to bring up the temperature by about 1F a minute, though. But given cooler water and a short washing time, this heating is practically useless.
I think from/including the 19, you got a heated Pre-Wash, the same Main-Wash heating as before (Except on ISE 23-series clones, where a circulate/hold was employed) and perhaps heated final rinse.
AFAIK, I've heard rumors that some of the lesser models in the 20-series actually did circulate during the holding time. I'm not sure as to how true these claims are. If so - it is worth looking into those models.