Cold hardiness value is quite misleading and there is no one constant temperature that can be defined for each variety. Rather, treat it as relative value to other citruses when exposed to the same set of environmental conditions.
For example, some would list Kaffir lime as hardy down to 34 deg F, but mine has survived more than a week's onslaught of 24 deg F and below, same with most of my other citruses. How do we reconcile such vastly different real life data?
The major difference is that my plants have been gently preconditioned to colder and colder temperature brought about by the nature of our winter climate. They have been hardened and went into near dormancy when some of the coldest nights hit my yard, of course, with my help of at least bringing the temperature a couple of degrees higher would tremendously help in tiding over.
However, when they regain active growth in spring, and there is a wayward arctic jet stream that could bring the temperature down to just 34 deg F, from a high of 80 deg F the day before, even my cold hardy citruses like Kumquats, Yuzu and Sudachi would suffer some nip in their new growth flush, and they are listed to be hardy to below 15 deg F. But those citruses that are still dormant, they won't suffer a nip at all.
So interpret the temperature value as relative hardiness to the same status of plants when they undergo such exposure. Their previous exposure, growth status within a given environment must all be taken into account, and that means one research institution or reference reporting them. It would be invalid to compare the results from Florida and California or from my yard to that of Benny's as what the lowest temperature these citruses could survive and for how long. Comparisons should be relative from within the same place, the same plant growth status, care, management. There is not one value that could be true for all cases.
Consistencies in the relative comparisons from various people would only give us an idea of their hardiness, but it will never be absolute.
