I've done many tests using the Holt's milk test. All of the testing that I can recall was on active or recently dead hives in spring, summer, or fall.
Can you do Holt's milk testing with reliable results for hives that died over winter and that have sat frozen in the bee yard?
I'm going out to inspect an operation next week and don't want to give bad results.
I know in performing this testing, or even when samples are sent off, nobody ever suggested that "samples must be from unfrozen hives or frames". So I don't think it's an issue. But wanted to make sure.