Why? Do you think that delaying the analysis will make a difference in anyone's conclusions? Do you think COVID will be over in March 2021? If not, why not do a running tally from April 2020 until the disease is eradicated?
Because they're talking about the number of excess deaths in a year. If it's in order to debate a question about Sweden's approach, it should be dated from when Sweden's approach diverged from the approach of others. And it should last 12 months, because that's how long a year is.
Are we now redefining now what a calendar year is just so that we can somehow get to the result we want? that's not science, it's not how it works. You're saying that even though for the past decades we're looking at mortality per a normal calendar year, now we need to redefine this, because the results just don't fit with our opinion and beliefs.