Most of the characters poeple are listing are only minor bit players. They are of no real value to the story and thats why they werent featured in great detail.
Does it really matter what Sollozzo was doing as a young man in Turkey? How does that effect Sonny learnig the family business?
Moe Greene building an empire in LV is somewhat errelivant to Vito becoming the most powerful NY Don.


If winners never lose, well, then a loser sure can sing the blues.