We really don't know of all those, or even half. A few don't even have identities. Informants like the one who was also doing killings, the gay man who went into witness protection may have done a few of those and blamed Senter. The government does lie at times. Also, to say "There are probably more" is just trying to up the number. Let's agree, 10 is more than enough. Yet all the time he has done, combined with others like Gravano being let out leads to his release being the same.
90% of stuff we know about the mafia is thru informants and indictments. He was involved in most of murders done by DeMeo crew, which is a lot more than 10, if you don't want to believe it, don't. He did few murders after DeMeo crew, for the Lucchese's
