It’s clear that the freestyle event in 2014 was very difficult and slow, perhaps the most challenging freestyle event since 1999, but 2001 and 2019 were also rough races. As mentioned in the discussion of the history of the classic race, The 2014 race was accompanied by heavy snowfall. It was warm and slushy in 2019, which slowed things a bit.
From American Birkebeiner & Kortelopet – 1973 to Present, in 2001, “Mother Nature sent the “Birkie Blizzard” dropping 8 inches of new snow from midnight til midmorning on race day,” producing a challenging day of the heavy snow accumulation.
The fast years were 2010 and 2020. Cold and firm skate decks were the likely cause. Temperatures were moderate.
There is a great website that provides a full suite of anecdotal accounts of Birkie races from 2011 to 2025 – BirkieGuide.com by Ari Ofsevit.