They don’t need the tapes, they have the press clippings. Nobody really cares what he said, what they care about is that it blew up into a giant kerfuffle that damaged the reputation of the league. A big part of the problem is that everybody has known Sterling is a jerk for a long time, there’s guy that cover the NBA pointing to articles they wrote about him 5, 10, 20 years ago. That’s really why this has blown up, it’s not the first time he stepped over the PC line, it’s not even the first time he’s generated press with it, but it’s now hit enough times that people are asking why nothing has ever been done about him before. Stern got really lucky he retired before all this since he was the commish for most of Sterling’s other incident, he’d have a lot of explaining to do; with him out Silver is free to ignore the past and deal with the now.
You are right about Sterling, but Silver stated specifically that his decision was based entirely on the recording, not on prior incidents. If the decision is challenged, he would not be able to bring in matters that he did not take into account in reaching his decision. I could see an argument that the decision was a breach of the NBA bylaws and the NBA would have no way to defend its decision. Its evidence is inadmissible. If they want to talk about prior conduct, they have to bring a new investigation, and reopen those prior acts. They may not want to do that, since they let those incidents go years and decades ago, and some of them were never proven.