Doesn't it go that when the first earlies flower, there are spuds below the ground? I don't know the science, but what I can tell you is the king edwards I left behind last year because I am a rubbish digger, have all grown and I have been happilly digging up little spudettes now for a couple of weeks, and as I need to room and dig up another, they are steadily getting bigger and more plentiful. What I would do (and will do soon) is just have a root around one plant and see what you unearth. you don't have to dig is up totally, just have a poke around with your hand and see if there are any yet. Good luck!