The USDA Plant Hardiness Zones  are based on the average annual minimum winter temperature. In former USSR agroclimatic zones were based on works of G.T. Selyaniniv (1928, 1930), who offered 3 parameters: sum of active temperatures (>10oC), hydrotermical coefficient, and average annual minimum winter temperature.

 the USDA hardiness zones are based on average annual minimum winter temperature. Agroclimatic zones in the former USSR were based on 1)sum of active temperatures (>10oC), 2) hydrotermical coefficient (relation between evaporated water and annual precipitations), and 3) average annual minimum winter temperature

You have raised a very valid concern. While average annual minimums are simple to calculate and do provide good guidelines, I would suggest that another important and critical factor that would sharpen precision in plant adaptability is the inherent genetic capacity to emerge from dormancy following periods of mid-winter warming. Our research on cryopreservation of dormant buds showed that  genotypes that lose cold hardiness after mid-winter warming, followed by severe cold temps, are frequently injured. Frequency of such temperature fluctuations may well identify regions that limit plant adaptation. This will likely accentuate if prolonged warm spells become more frequent, as many have predicted with changing climatic conditions.

Thank you very much for your suggestion. Could you please suggest some way of measuring or quantifying this situation also?

From a taxa standpoint, one could conduct controlled de-acclimation/freeze test studies to identify susceptible cultivars and species, by exposing dormant twigs to warming for prescribed periods, then freeze test them to evaluate injury. From a climatic standpoint, looking at weather records to identify locations that are more or less routinely subject to mid-winter warming would be one suggestion. A modified growing/degree day calculation may work to quantify vulnerable regions, such as foothills near mountain ranges.