The number of impressions in the Global report is not necessarily the same as impressions in the Content reports.

The impressions metric we obtain from LinkedIn API is the same but it is displayed differently in Global tab and in Content tab of the report.

The impressions shown in the Global report represents all impressions received in the given time period (it can include post outside of the selected time period). For example, a report run for 1st Oct - 31st Oct will show all impression received in that time period (regardless of on which posts).

In the Content report we show the impressions per post. So we show each post in the selected period and show the total impressions that post received, regardless of when they came in. For example, a report run for 1st Oct - 31st Oct will show the total impressions on each post published in that time period.