I have heard that on one occasion the Blessed One
How do we know who this author is? Is there general guidance on who to attribute the suttas to?
A council of 500 Arahats was held at Rajgir (Sanskrit: Rājagaha) to agree the contents of the Dhamma and Vinaya. Ananda recited the Suttas, such that each begins: ‘Thus have I heard’.
Most of the back stories are included in the commentaries. For English readers I recommend Mr. Piya Tan's translations and commentaries which are available at www.dharmafarer.org