I never said a pot plant will add more leaflets. Pot has a compund leaf structure called palmate. The leaflets will grow longer though. Honey Locust are compund as well but their structure is referred to as pinnate. So that seedling you have there actually only has two leaves. And just as pot leaves grow longer, so to do the HL leaves. Being pinnate, that means they increase in length by adding little pairs of leaflets. Here is a picture of a tray of Honey Locust demonstrating the variations in seedlings.