But my point here is not to prove that they have done so, but that Bosch's paintings were often like a patchwork of mini paintings and that this was common practice around 1500 AD. In this print, i found a detail that was repeated elsewhere. Somewhat to the right at the foreground, among the many funny-looking monsters, a little guy is leading a parade while making a phallic*) gesture.
The same guy turns up at the feet of Saint Christopher on another print by Duhameel! Without the flag and the dragon's tail, but it's the same character.
It's now easy to imagine Bosch and his family collaborating on their paintings by piecing together several designs and sketches, in stead of the cliche'd situation of the master who designs everything and then leaves the boring bits to be painted by assistants.
Many elements from The Garden of Earthly Delights look like intials from manuscripts anyway.
One problem i am still left with is how paintings were copied on a different scale. I suspect some sort of pantograph ('tekenaap' in Dutch, or 'drawing monkey') was used, but the official reading is that it was invented roughly a century after Bosch's death.
*) Possibly the sign of Asmodeus, but not sure about that.