Facebook divides reach into two types: organic and paid. However, there used to be a third reach type:
Viral reach
"The number of unique people who saw your post or page mentioned from a story published by a friend."
As this is basically the same as people seeing the post organically, Facebook decided to combine the virally measured reach with the organic reach in their interface. In the API they have not done this yet. This means, in Swydo we still have viral and organic reach separately available.
So, to get all of the organic reach, you have to add both viral and organic reach to your widget!
Note: when manually summing organic, paid and viral reach the result will be equal or higher than "Post reach". This because a user could have seen the post multiple times, counting as e.g. organic and viral separately.