Without checking my notes the reason for a single Roud Number could well be because those variants you mention are closely related through intermediate texts.

Generally speaking we often group variants together that have more than 50% of text in common but sometimes outliers can have less than that in common if once linked by intermediate versions they are demonstrated to be basically the same song and to have come from a common origin, usually the broadside versions but not in every case.

This becomes more complex often when texts come from America that have been reshaped. If the new shapes contain significant new material we refer to them as ecotypes and in more extreme cases give them a new number. A good example would be Unfortunate Lass/Lad/Sailor cut down being rewritten as Streets of Laredo.