Interesting question! I took a look at the past few years and found these four at the end of the season: Cherry Blossom Song, Edith Wolford, Sponsorship, and Stairway to Heaven. My favorite oldie, Pink Lace, is usually there at the finish also. And Autumn Tryst has frequently rebloomed right along with the early daylilies.

No re bloomer here! but my latest bloomer were First Blush, Night Owl and Glamor pants. Harvest of memories bloomed all through the season. My Gallery is in order of Blooming.

Here is a link that might be useful: Gallery

The historic iris Shah Jehan (Neel 1932) is one of our latest bloomers.

In my garden, Spin-Off and Maid of Orange bloom in June. No Count Blues and Cajun Rhythm bloom in June and into July. New Leaf, Total Recall, and Recurring Dream rebloom in early July at the same time that No Count Blues is finishing up.
Renee in CA.