I ran some of the calculations on various sites and, apparently, I'm only supposed to put seven pounds on the span. How in the world are supporting 24 pounds??? Again, I've had no issues for almost 20 years, but now I'm wondering if this is an accident waiting to happen. I can add some more supports, but I just wanted some thoughts on why this hasn't catastrophically failed already.
I've included a photo to show you the current setup.
更新1:
As I mentioned earlier, I'm not certain if the shelves are tempered or not. I know the front piece is tempered because there's a mark indicating as such. The shelves do not have the stamp. If you run the calculations using annealed glass, the weight limit drops to 16 for the whole shelf (or 8 between each support). That's what's blowing my mind.