You're right. Floyd probably always entered and left the bar through the servants entrance.
If there were only two doors to the place, front and back, perhaps the back was only used for deliveries, and as an emergency exit. Most likely he entered the same door as every one else, whatever shift he worked. And that’s a question that should be asked, but hasn’t been answered yet. Did they work on the same days, nights? Did they work on the same shift? People claim the owner held meetings with employees, but did he keep a record of who attended on what date? It’s all up to speculation at this point.