When it's a Beaugnier.
Before I sold saxpics.com, I had found a few horns made for SML prior to 1935 from Rene Guenot and I've had to deal with people saying that SMLs were made by Buffet for years (they're not), but while researching something different, I stumbled across
Yup. It's a Beaugnier-made horn. Doctorsax does a good job with posting comparison pics of that Vito to make his case.
Please note, however, if you decided to play around with the serial numbers on http://www.doctorsax.biz/beaugnier_ser_nos.htm, that he doesn't differentiate between the Leblanc System (two versions), Rationale (whichever spelling you wish) and Semi Rationale (two versions). However, the Beaugnier serials he lists tend to suggest that this horn was made in the 1970s.