Right, but wouldn't that depend to some extent on location? A late in Florida would allow more time for rebloom than a late in Ohio?
Whether any cultivar is able to rebloom will always depend on the length of the daylily growing season.
Whether a late flowering daylily in a location with a long growing season would allow more time for rebloom than a late in a location with a shorter growing season depends on the definition of the daylily bloom season. If a daylily can flower during any time of a long growing season then the cultivars that flower near the end of that long growing season would be late flowering and should not have much if any advantage for rebloom over a late flowering cultivar in a location which has a shorter growing season. If the daylily bloom season is only part of the growing season then daylilies that flower in the late part of that period may have a longer period in which they can rebloom. How much of an advantage may depend on why the bloom season is considered to be shorter than the growing season. If there is a period during which environmental factors (such as high temperatures) prevent flowering (or development) then there may or may not be an advantage.
The flowering season is divided into seven time periods, EE, E, EM, M, ML, L, VL.
The daylily dictionary defines them as "That portion of the growing season when a particular cultivar is in bloom. The seasons are categorized in rather loosely defined periods, such as: EE, extra-early – the earliest flowers to bloom; E, early – overlap or follow slightly behind extra-early bloomers; EM, early to mid-season; M, midseason; ML, midseason to the beginning of the later portion of the bloom season; L, almost the end of the bloom season; and VL, very late – the last flowers of the bloom season."
If VL means "very late - the last flowers of the bloom season" how can any cultivar registered as having a VL bloom season rebloom in any location?
I assume that hybridizers decide that the daylily bloom season does not include all of their growing season even though daylilies may flower during the entire growing season. Presumably they divide the growing season into a portion during which daylily cultivars bloom for their first time and the remainder of the growing season after the last cultivar has bloomed for its first time.