Well, we've just known about Anokata (the current boss) being cautious, Renya might not have been that cautious after all. I said that after Renya had died (or had been killed), Anokata replaced him as the leader.
My speculation is that the Crow Association (possibly original BO) when first established, was just a wealthy & normal association (not an evil syndicate), therefore Renya didn't have to be cautious. But after his death, the Association went downhill, probably because of finance problems (which explains why the 2 strange men had to steal everything, they might not know of the "big treasure"). At that point, Anokata took Renya's position as the Boss and began to run the Association the illegal way instead (including robberies, murders, black-mailings...) in order to maintain it. Since Anokata is cautious, he probably spread the rumor that the CA was gone after Renya's death to avoid public's eyes and the press...
About the crow symbolism thing, I'm not really sure. It's probably another mind-trap set up by Gosho. He may want us to think that the idea of using "7 children" was come up by either Renya or Anokata, but I highly think that it was inspired by someone else. It would be a shock if this method was inspired by Gin...