The devastation is (sadly) amazing, Lorn, and the variation remarkable. I would imagine your cold temp reading of 26-27°F is only ball park for all your gardens.
Predictions for my area was only light frost, and I had 9 mph wind. The only damage was on a Aralia coradata var. sachalinensis at the upper right.
Trumpets were fine. These pics taken days after:
Contrast the damage you had on trumpets and aurelian lilies at circa 26° with "damage" to a martagon section lily at 24° (2015):
And by the end of the day, they had perked right up. Not even any flower bud loss on these later in the season. (Although in a different garden, I did lose some flower production.)
Martagons can laugh at 30°!
Some cold hardy perennials physically remove water out of of their above ground parts in response to cold, and temporarily move that water into underground structures. This increases their ability to withstand colder temps by concentrating the antifreeze chemicals in the leaves and stem. (Less water means less dilution of those chemicals.) This is what is happening when plants droop excessively in the cold and perk up as if nothing happened when it warms. Contrast that with cold damage, when return to normalcy doesn't occur.
