If they are going to approve the leaves in seniority order, they have to have some cutoff. They can keep offering again, but it probably just saves administrative hassle doing it once a month.

As for the furloughs:
I used to be at an outfit that had a pretty good furlough clause. If they announced an involuntary furlough, they were required to simultaneously offer a voluntary one. It was equivalent to an LOA. Seniority, longevity, travel and health all continued as though you were active (except JS). Anyone who took the voluntary furlough, replaced an involuntary one. It saved quite a few involuntary furloughs.