Gingertom,
The reduced schedule was conservatively built and then increased as more cabin crew turned up for work than in the plan. This happened in the first two strikes and has happened again in the current strikes.
When rebooking pax in the WDC, we were given lists of reinstated flights. Some were freighter flights which became passenger flights once enough cabin crew turned up for work, I guess others would have been genuine cancellations which got reinstated once the aircraft and both sets of crews became available.