You are asking questions that cross the discussion.
Only around 1-2% of Tweets globally have location data attached. This does not differ across our delivery mechanisms (REST, Streaming or Enterprise Gnip)
The Twitter Search (REST) API has an additional limitation that the index is optimised for recency and has a 7 day look back window.
If you are filtering for terms on the real-time API for your given radius you may receive all the Tweets in that geo but there is no guarantee of this.
For high fidelity data you should look at Twitter’s commercial Gnip data APIs, or go via a partner.