Again, why would this stroke of "luck" be limited to Oswald?
You do well to put the word "luck" in scare quotes, Mr Smith!
If the absence of any employees on the sixth floor benefited a Lone Nut gunman, then he got incredibly lucky (no scare quotes needed).
But if the assassination was a planned conspiracy, then the idea this "luck" (scare quotes needed) would have been left to chance is absurd.
Furthermore!
A Lone Nut employee-gunman would have been suicidally stupid to choose the sixth floor, for he would have known the high likelihood that he wouldn't have the floor to himself. He would have chosen the rarely-visited seventh floor: