Who was doing controlling the air space in between those times?
On August 5, following the PATCO workers' refusal to return to work, the Reagan administration fired the 11,345 striking air traffic controllers who had ignored the order, and banned them from federal service for life. In the wake of the strike and mass firings, the FAA was faced with the difficult task of hiring and training enough controllers to replace those that had been fired. Under normal conditions, it took three years to train new controllers. Until replacements could be trained, the vacant positions were temporarily filled with a mix of non-participating controllers, supervisors, staff personnel, some non-rated personnel, military controllers, and controllers transferred temporarily from other facilities. PATCO was decertified by the Federal Labor Relations Authority on October 22, 1981. The decision was appealed but to no avail, and attempts to use the courts to reverse the firings proved fruitless.
From: https://en.wikipedia.org/wiki/Professional_Air_Traffic_Contr...
Then a lot of new hiring afterwards.