I planted a Mayfield Giant Coreopsis last spring. It grew very well and bloomed it's head off all summer long. I did deadhead it too.
It's planted in a bed on the north side of my house but gets sun almost all day long especially in summer.

I left it up all winter and then cut back this spring to about 6 to 8 inches (the dried up stalks, just so I would know where it was).

It hasn't shown up a peep yet. Should I be worried? I don't want to plant anything else there yet if it has a chance to appear yet.