Adina, I believe that orange cosmos is hardier in general and a more reliable reseeder.
Ms. Scott, I'm having trouble with the visual... you sow them in pots with a plastic bag over when you sow them so birds don't eat the seeds you sowed? Cosmos seeds aren't don't need light to germinate so it's fine to cover them with 1/4" of loose soil; will that be enough to keep the birds away? If you're saving the ripening seed for birds when they mature in the fall, I need more information and I'm completely confused.
Just so the birds and other squirrels don't take the seeds:
I sow them onto large containers and pull a large clear plastic garbage bag
down over the container--fasten with clothes pins on the rim of the container.
Sometimes use a stick or ground staples just so bag does not blow away in wind.
Yes, the seeds are covered with soil
but the birds and squirrels scratch them out.
The bag helps to keep the soil moist also, but allows light for when they sprout.
Sort of large size winter sowing.
I'll take a picture when I sow them again next year.