Question about Unique visitors count

Hi folks!

Everything fine with matomo, thanks to Matomo dev team for nice product. Only one thing which I can’t understand how Matomo aggregating unique visitors count. For example, we use log import feature (we are importing web server logs to Matomo application), if I take first month when we start using matomo I see about 20 millions unique visitors for that Month.

Question 1. I assume, since we just started use Matomo, probably all users are unique except those who visit site again during that period?

Then every month this number decreases, for example 7 months later I see 7 millions for same period “month” with bigger visits & pageviews count.

And finally, If I take last month (August 2019). I see about 2 millions for period “month”.

Also, if I take period “day” or “week” for same month, for example August 28 I see probably same number ~2 millions. Can someone explain this?

Question 2. So how to interpret month results? I suppose month results = unique users sum of all days of given month?

Question 3. Why unique visitors count was so big on first months when we start use Matomo?

Thank you in advance!

Anyone? :slight_smile: