If they are already loose now, it won’t get any better over time. I would screw everything “rock solid” anyway. Take them down, drill the hole in the center, and done. With proper tools, you can leave a 20 mm edge. I wouldn’t place it in the middle between two boards (there are also pictures of that). Besides, where do you place the drill? In the joint? :rolleyes: Show the current situation, where the hole should go.
No, nothing is loose. I just had screwed a board incorrectly and had to remove it again. Then I couldn’t mount the same board with the pre-drilled holes in the exact same place with the screws. I took a new board and then shifted the drilling slightly. Still, this teaches me to try to leave the boards on first. Otherwise, everything holds rock solid. The lights are also on the outer edge. No one will seriously or regularly stand on them. I am more concerned about what the 2 cm of wood alone will do over the next years. With a 105 mm hole saw from Bosch, I am well equipped in terms of tools. I almost tend to make the 105 mm hole centered after all. Because, as you already said, I can’t set the centering drill between two boards either.