You may occasionally see some rows in your Google Ads report display not served in date range. In cases where the session is attributed to a click that occurred prior to the date range you selected, the report displays zero impressions for the campaign, ad group, or keyword.
A common reason for sessions with zero impressions is users coming to your site via bookmarks. For example, a user may click on an ad, and then later, during a different session, return directly to the site through a bookmark. The referral information from the original session is retained in this case, so the one click results in multiple sessions for a single campaign. If the user continues to return to your site via the bookmark, the campaign doesn't register any new impressions even though it accrues new sessions because your user is not reaching your site through the ad.