>> Will those plants still actively and continuously flower
>> all the way til the first frost in October or early November
>> like here in Delaware?

Yes. Last year I started about 15 dahlias of various types in pots in my greenhouse about 2 months before last frost. They both bloomed much earlier than tubers planted around the last frost date and they continued blooming up to the first hard frost. One was Kelvin Floodlight which makes large AA blooms. It bloomed right up until frosted. Our last frost came later than usual at the very end of November and I was giving some plants frost protection as well to extend the season. I did notice that both quantity and quality were dropping off toward the very end and I believe this was due to lack of sunlight at less than 10 hours per day. I got loads and loads of tubers from the long season plants probably due to the many short days. I divided one clump of Le Baron that had around 40 tubers though not all had eyes.

40 tubers from one plant? Wow! I was forced to grow almost all of my dahlias in 5-6 gallon pots last season for the first time, and contrary to the info given at the top gardening sites, large dahlia plants do not do anywhere near as well in pots than in the ground . The plants were thin and kinda spindly, the size of the flowers were significantly dwarfed, and there were much fewer of them. But also the tuber production was lowered and the tubers were about half the size that they would've been if they had been grown in the ground. I could write a novel with all the bad dahlia growing advice I've gotten off the Internet gardening sites(except for here, which is usually good info)

I'm surprised Steve got that much production from Kelvin - my Kelvin only produced about 12 flowers but it was its first year so I suspect it is just getting used to its location.

That said, I was going to answer that how long a dahlia will bloom depends upon how large the blooms are. I read elsewhere that many of the larger AA's expend so much energy blooming that you might only get 8-12 per year. But smaller 2" blooms might give you hundreds. My personal experience matches that - my 2-3" Patty Cake will bloom for 5-6 months but my 10" Baarn Bounty only blooms for 2. I get over 100 blooms from PC but only 8-10 from Baarn.

I didn't mean to imply that I got a lot of flowers out of a single Kelvin Floodlight, maybe 15, I was only saying that it started blooming early because I gave it an early start in a pot and then transplanted it into the ground and it continued blooming until late in the season. Like David mentions, the dinner plate varieties don't produce a huge quantity of blooms. I think my top producer was Maarn (class M) which I orginally bought from Swan Island. I lost count of how many flowers I cut from it but it was quite a lot, maybe 30+ from the best plant. Note that it had many more buds and blossoms than that but for cut flowers you can't always use every flower due to misshapen flowers or stems that are too short. Sometimes I also strip buds off to make smoother stems.

I got a fairly long bloom season the year before last with Vassio Meggos bought from Swan Island. It's listed as producing 9" flowers, but I allowed it to grow 3 main lateral stems after topping at 3rd leaf level, and I didn't do any disbudding, so it didn't grow any 9" flowers, but they were usually averaged from 6 - 7.5". Oddly, once late October rolled around, Vassio Meggos actually started its most prolific bloom phase to date, with 8 flowers on it at once! Unfortunately we got our 1st hard frost on like Nov 2nd, which wiped most of them out before they had fully opened. I'd say I got a total of 20-25 flowers on it in the 2 months it bloomed. But on my one Freckle Face plant from Swan Island 2 years ago I got 80-100 flowers of 3 - 3.5" in nearly 3 months of blooming, and its listed as a 3" flower producer, so even with 6 laterals, almost no disbudding, it still always grew flowers of at least 3 , at least til the end of October when the suddenly got small due to the colder weather and serious lack of sunlight.