I think it's possible that Sirius know Bellatrix was associated with this gang. One possibility is Bella was the former leader and Regulus joined this gang and mentioned something about it.
That doesn't make sense. Regulus is a year or two younger than Sirius. Also Sirius specifically mentions that Bellatrix hung out with Snape. He was talking about Snape with Harry, Ron, and Hermione so it wouldn't make sense for him to bring her up if she was not there with Snape. Personally I tend to take the dates on the family tapestry lightly as it is full of contradictions. You're only supposed to blow the bloody doors off! (talk) 02:32, May 12, 2014 (UTC)