Funny you should post this: I was just weeding today and pulled a 4" sprout that I'm 100% sure was a cosmos which I haven't grown in 2 years. I wish I would have left it!
Woofie, I pull Bachelor Buttons "centaurea montana" like they are weeds because they also reseed and take over here. Nice blue though
Forget-me-nots are another thing that are weed-like and keep overwinter way too easily.