I thought I would do the same comparison. To attempt to get some critical mass, I added orienteering and running and called it running. Totals for December each year: 2015 running 7, skiing 0. 2016 running 2, skiing 0. Not sure what is says, but there wasn't much skiing going on either year. Or all that much running.
Perhaps Christmas Day was not included in the current month this year, but is included in the comparable month in 2015. Therefore, this month's training volume is somewhat overstated compared to 2015.
Around here, we make a point of capitalizing on all the days that are capitalized. Even Daze are capitalized on most occasions.