In my previous post i forgot to mention that eventhough the gun in post 1 has more than one touch hole, this would not always mean that every shot where to be ignited seperately. This would not make sense either because we can clearly see the holes in the clodshot. Combined with the knowledge that early gunpowder was indeed fine dust like powder, it is to be expected that the holes filled up automatically when the next load was put in. This makes a chain reaction from the top possible.
As to how the pieces where inserted, i still believe they had to be hammered in to some extend. Medieval barrels where far from smooth and if such a piece of clodshot would just slide in the gas loss would have been enormous.
And maybe they did use some sort of measurment stick to determine if the powder plus shot was fitting in between the two touch holes.
Within this theory it is possible to shoot 1 or 2 or up to 5 shots (post 1 illustration). I don't know of any gun that has multiple touch holes like this, nor of a loaded gun with more than 1 piece of clodshot. Michl had a tillered hand cannon which held 1 shot and a large load of powder. Other than that there are few examples of surviving loaded hand cannons, at least not known to me