I think that is right. I believe before the plug cap, they did use a screw in Edison base like we see on a light bulb today. That goes way back tho. Pretty hard to make TR I suppose, especially at baseboard height.
Keep an eye in the baby
I am actually surprised that the Edison base socket has lasted this long in this safety conscious world we live in now. I guess there is just too much installed hardware out there for a change.