Yup interesting question on losses there Mick...if a hive makes it through the winter with a queen but she is a drone layers/ unmated virgin from late supercedure previous autumn or like yours running out of sperm ....do they count as winter losses? The exact same thing can occur in any hive at any other time of the year so they are not specific to winter.
I have one hive which on 1st inspection had a queen 4/5 BIAS etc etc. Last inspection no queen seen no brood, no queen cells.....test frame added. Is that a loss....1st inspection would say no, second would say ... probably a loss...
We need a better definition of what a winter loss is.
To me it's simply a hive that went into winter and died or a hive that went into winter queenright and ended up with a mere handful of bees left inside and no queen. All other scenarios are not really losses specific to winter, just losses that can occur at any time of the year.
To go back to one of Adam original points about whether winter losses vary in poly vs wood. I don't think we have had any cold enough winter s recently to really test that. In the mild winters we have been experiencing wouldn't expect much difference, except lower store usage in poly hives. -7C was Yorkshires coldest temperature this winter/spring recorded in Swaledale in April this year
What I do know from an old Finish beekeeper where they have extremely long cold winters -12 to -20 C are regular nightime temps......everyone uses poly hives. Many even use reptile heaters cables to keep nucs alive.