Each class of rebloomers has a seperate trigger for its rebloom.

"Whenever" such as forever Blue  from whenever it reaches maturity   fromend of  regular bloom time + 1 week until frost, whenever a    fan reaches maturity

Summer(direct)  Rebloomers  after maturity (about 6 weeks after spring bloom)  and when 6 days of min temperatures are in 15-21 C range, with about 3 weeks to mature flower stalk

Fall cyclic- when plants mature and night time length exceeds treigger length, plus 3-4 weeks t omature flower stalk

"Facilitative Vernalization"  when plant has been at maturity for an extended time (about 4 months).

A  Fall cyclic  rebloomer may not rebloom if it has a high leaf count maturity and slow growth.   Thus is a Fall cyclic rebloomer , but not  be able to muster resources.

A Fall cylic rebloomer is  mismatch of aphylla genes (photoperiod dormancy and no vernalization genes)  with cold dormancy and vernalization genes of regular bearded iris. Thus if you cross suitable plants, you could get a Fall cylic from parents that produce children mismatched for these gernes. That is one parent has one set of genes , and other parent has the othe set.   Often seen in a cross of aphylla with regular TBs or particulaly in F2 of this cross.

Chuck Chapman