The notion of time lag in the counting of deaths corresponds to the fact that all declared deaths are not counted instantly.
The data we provide comes from death certificates.
There are several reasons for this:
The time for the human to perform the death
The case of missing persons
Some cases must be settled by a court
Thus, death data is never frozen .
In December, there are many deaths which are counted the following year given the end of the year, there are about 25% of unaccounted deaths over the year. On the other hand in November, this rate drops to 1%.
Concretely, it takes 2 months for the data to no longer have significant changes.