Sample of all non-paid visits (Google Analytics API)

Question

PHP

The task is to select the number of free visits where the user has moved from the search engine.
In general, select the information that is displayed on the Google Analytics page if you go to the menu "Traffic Sources -> Search Engines" and select "Show: unpaid" there.

Based on the Google documentation:
code.google.com/intl/ru-RU/apis/analytics/docs/gdata/gdataCommonQueries.html#traffic-sources
Wrote a query like:
code.google.com/intl/ru-RU/apis/ analytics/docs/gdata/gdataExplorer.html?ids=ga

: 26681302&dimensions=ga:hostname,ga:medium&metrics=ga:visits&sort=-ga:visits where medium=organic).

The total number coincides with the data in the Google Analytic admin panel, but the number of visits from search engines is less by an average of 10-20k visits.

On sites with low attendance (up to 1,000,000 per week), the data is completely correct, but on a site with more than 3,000,000 such an unpleasant error turned out. Maybe someone faced a similar problem, maybe Google takes not only organic into its selection?