I've been playing Adventure since about 1981. I have played it a lot.
Tonight, something happened that I don't think I have seen before.
I started the game - variation 3 - went down to the right of the maze in the White castle area and found the sword. The Green dragon came down from the room above and I killed him. At that point the bat swooped in and took the sword.
I went to the White castle, found nothing and headed to the blue maze. When I got to the 2nd screen above the blue maze entrance the yellow dragon was sitting there dead. In other words, either the dragon had run himself into the bat with the sword or the bat had killed the dragon with the sword.... I think?
I tried searching (for discussions) of this happening, but couldn't find anything - this certainly seems possible, but I would have thought there would be limitations on which offscreen objects had collision checking code.