I'm still learning about Monarchs. I knew they produced multiple generations on their path southwards. I didn't know that the generation born in Fall actually flies all the way to Mexico, overwinters and then mates to produce the first generation.
Here are two great links about the Monarch generations:
Monarch Lab and Monarch Butterfly USA.
I'm still seeing Monarchs pass through our yard. It's Oct.20th and the clouds are breaking up. Sure enough, I found another Monarch on the butterfly bush a moment ago. The photos are too dark to use though. The lantana, butterfly bushes and coreopsis plants are still blooming in late October. Maybe, we'll get an Indian summer after all. The Heavenly Blue morning glories which normally bloom in September are starting their show in October.