These numbers are difficult to pin down. Hive strengths vary with economics. Pollination has had a huge influence, and honey prices affect how much is extracted and how much is left for feed.
There is less wild forage, and land use changes. Plant breeders change the nectar production.
Many other factors enter into it, too.
Like many other statistics, the averages hide a lot of detail and may or may not have meaning for any particular purpose.
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