People often look at leaderboards or post data within CrowdTangle, compare it to Insights, and wonder why the numbers are different. The answer is that we're measuring different things.
When you select a CrowdTangle timeframe, we measure interactions (including video views) that happened on posts that were POSTED during the timeframe, no matter when the interactions occurred. Facebook Insights timeframes for video views look at views that OCCURRED during the timeframe, no matter when the posts were posted.
For example, with a timeframe of July 2017, CrowdTangle will show you the view totals AS OF RIGHT NOW for posts that were posted in July 2017. And if you looked at that same leaderboard in a month, the numbers would likely be higher, as those same posts amassed more views. For that same timeframe, Insights will show you the views that happened during that month, even if the views happened on posts that were posted in 2016, and as of August 1, 2017, those numbers will never change.
So what am I supposed to use?
The answer depends on your purpose. If you're looking for competitive analysis, CrowdTangle gives you apples-to-apples public comparisons between your page and pages you do not own. However, if you're looking to see deeper data about your page in isolation, Insights gives you far more private information than you can get via CrowdTangle.