The problem for many of those variables is that they will or will not be proved right only in hindsight.
When starting out the big question is how much stores to make sure they have. If you only have one hive then the cost and work in giving a bit too much is hardly an issue. A bit too little means they probably run out in Spring, which is exactly when they are in a critical state - as Mick points out.
Older bees dying off, younger bees being raised, uncertain weather - not a time to be short of pollen or carbs.
So for one hiver’s , within reason don’t try to be too accurate, ask locally what others do and start early with practising hefting hives in various conditions. It’s amazing how quick muscle memory develops and gives you either some reassurance or grounds for investigating further. And don’t be inhibited by snotty comments about feeding spring feeding fondant / syrup, if they really are light come spring. Do right by the bees in front of you.
As others point out, there are plenty of reasons why they may have used more or less than reasonably anticipated.