I'm not sure only having one isn't very unusual, as opposed to ordinary, however considering the royal family essentially would have had their trees mapped for them, and having had it done so for a very long time, as it is central to the nature of what they do, in order to even do something equivalent, it requires mapping ancestry and other lines that aren't always going to be immediately evident.
I guess it depends on the gateway ancestry - my own is the Staffords (Grafton) to Audrey Barlow - and there is another Stafford with not much history in Britain that married into the same family after arriving in New England in the 1600's.
I've read about it not being uncommon to have multiple gateway ancestry when someone has a fair number of early ancestry in New England (in my case it is all Great Migration -not Mayflower) -but I haven't found any other than Audrey Barlow (Almy).