In Saltybees #20 post the broodless winter period seems to throw possible shade on some premises. Strange that this is not something more often discussed! We know the results of LW's but dont have a clear answer about the cause (or combinations of causes) necessary to initiate it. Apparently there is always some laying workers in a colony. Enough perhaps to keep the story alive that workers can move eggs!
It is often said that LWs usually takes three weeks or more after last brood has hatched before it shows up. I have only had a few first hand experiences with it, so take that for what it is worth.