Citradia, That's a shame (Swingle).
All my citruses (including Cold Hardy) are in containers and are hidden in really strong frosts. They are primarily intended for planting in the ground. My biggest problem is that the garden is small. First I have to make a new roof on the house and then I put the citrus into the ground. Otherwise they would be destroyed during construction. I have no other place to store the material ...
Frost resistance is currently tested on these plants in containers. Last year they were hidden at -16.1C. Under -12C was only two or three hours, but the previous two weeks was a frost with several recurring temperatures -12C. Outside were Rusk, Morton, Swingle 4475, USA119, HRS899-A, Unshiu X PT ITSZ Prague, clem. Crete X Troyer, Changsha. Everything, beyond the HRS899-A, did it only with minimal leaf damage. But in the spring the plants sprouted later and had only small increments. My citruses generally have a higher frost resistance than is stated. In some cases, it is really significant. Why? I do not know.