Don Firth, many thanks. You have answered my question, which was not about Lanza's history, which I knew in its basics, but about how the various opera reference books could ignore him. Especially when he was originally "discovered" and brought to Tanglewood by none other than Serge Koussevitsky. But now I think I understand: to serious chroniclers of opera, he was not a true opera singer, so he is excluded from their listings. I *am* surprised at the Britannica, however, which lists Elvis and Frank Sinatra -- seems to me a mention of Mario Lanza would have been in order.