I knew someone who was in one of the first OTS batches right after the strike.
The situation was much "easier" - there were far fewer flight ops, fewer sectors/areas to learn, managers at the time were semi-competent and could train replacements, and there were enough military controllers to fill the gaps.
Even then, smaller facilities were temporarily shuttered, capacity was reduced bigtime, sectors were combined and greatly simplified, and spacing requirements were basically quadrupled. Took probably 2-3 years to get to around 80% capacity.
I remember my buddy telling me that when showed up to his Z, there was no backlog and he would be trained around the clock - checked out in record time. Right after he certified, he would train non-stop until the early 1990s when he left for another facility.