It looked like I was able to connect two nodes to each other multiple times. I will admit I found this out accidentally as I was trying to connect to others and my input was misread (playing on mobile). I was thinking that would not be allowed, so was surprised when it was.
More generally, and likely a user specific issue, my phone either kept either refreshing the page or navigating back in my history while I was trying to set up the edges, making me lose all progress.
Regardless, I did have fun with the concept.
The undo/redo buttons were very helpful, I was certain I had figured a test out but ended up being wrong. Being able to go back to the assumption I made early on instead of having to restart was much appreciated