I'm not so sure. What you say makes sense, except for the fact that the yellowing has been going on for at least four weeks now. I only put the extra 2 in 10 days late. If your theory were correct the extra 2 should have started to yellow at least 2 weeks ago. Or am I missing something?

To date, still no sign of yellowing what so ever on the 2 SuperPlants. 50 days now. Any other ideas?