I wish I knew the answer to your question. I hope someone who has the answer will let you know. I do not plan to winter sow any annual seeds, only perennial. Some perennials probably don't need to have cold stratification but I put them out to try to get a jump on their sprouting as soon as possible.
I did a few more jugs today. This time I planted Hollyhock. I did 7 different jugs/different colors but I know that they may not come true to the color of the original plant. One jug was Dwarf Hollyhock and one was from a trip we took where I collected seeds of unknown color. So far none of my jugs used have been milk jugs. I have used other plastic contains such as coffee creamer bottles, booze bottles, juice bottles, bigger size water bottles, and even a catsup bottle. So far 38 of them are done and outside except fir the last 7. They will go out tomorrow.