There is a discrepancy for certain emails between Email Insights and Email Performance Report. The data (e.g. sent, delivered, opened and clicked) are significantly lower in Email Insights for the emails as compared to the Email Performance Report for the same emails.
There is most likely a discrepancy because at the time Email Insights was first enabled "you’ll have four weeks of historical Email data in addition to all new email activity". There was no request to Marketo support to upload historic data beyond four weeks which would have included data for the emails above. This request relates to the notes below from the article:
"We’ll give you a four-week period before you can request Marketo Support to upload your data"
The solution is to request that Marketo Support backfill the report data so you have data for Email Insights beyond the four weeks.