The December 2020 core update ran from 3 to 16 December 2020, taking 13 days. It was widely reported as one of the largest core updates of that era, and it ran straight through the peak trading fortnight. Google shipped it anyway, which was unusual then and became the pattern only much later.
A large update at the worst time of year
Reported movement was broad and substantial across most verticals, with YMYL sectors again showing the sharpest swings. For ecommerce sites the timing meant a demotion landed in the two weeks that carry a disproportionate share of annual revenue.
Google generally avoided the retail peak in subsequent years, holding updates until January, until the December 2024 pair broke that convention. December 2020 is the earlier exception.
The seasonality problem, in reverse
December is the one month where a traffic increase can hide a demotion. A retailer whose traffic rose 40 percent year on year in December 2020 may still have been demoted, because seasonal demand masked the ranking loss underneath.
- Compare year on year, not month on month. December against November tells you about Christmas, not about rankings.
- Watch average position specifically. Demand lifts clicks and impressions while leaving position alone. A demotion moves position even when clicks rise.
- Check January. If traffic fell harder than the usual post-Christmas drop, the demotion was there all along under the seasonal lift.
Diagnosing this now
Search Console holds sixteen months, so December 2020 aged out in early 2022. What remains useful is the principle rather than the data: any December diagnosis needs a year-on-year comparison, and any site that felt fine through a December and collapsed in January should look at the update that ran in the middle.
More than twenty core updates have run since. A site still carrying damage from this one has been reassessed repeatedly with the same outcome, which points at an unresolved cause rather than at bad luck.
Traffic looked fine in December then collapsed in January?
That is the classic signature of a demotion hidden by seasonal demand, and it is routinely missed. Send your Search Console access and I will check for it.
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Traffic dropped around Dec 3, 2020?
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