This is 'Double Triple Treat'. It is an older one and I put it up to show how in drought and/or colder weather, double daylilies sometimes aren't really double, but rather have just a few extra petals or a 'puff' in the center.
'Double Sunday' is what is called a hose-in-hose double, where there are layers of petals, one on top of the other with a classic daylily shape rather than something that looks like those tissue paper carnations we made when we were kids.
This is 'Double Bold One' which is a large flower and really stands out in the garden.
'Double Barrell' is another older flower. Funny how some of these older ones, now considered historic daylilies, were ones that we bought as new introductions for prices we thought were astronomical at the time but which wouldn't make someone bat an eye now.
This is 'Prester John', another mostly hose-in-hose, though it often gets a little puff in the center in addition to its layers of petals.
Though I like doubles and grow many of them, they can be more difficult in the north than in places like Florida where so many of them are hybridized. Doubles there are sometimes singles here because of the climate differences and cold or cool weather and lack of rain can also keep them as singles. That said, they are still lovely flowers, even if they don't have quite the number of petals each time they open.