User blog comment:MeerkatQueen/List of VOCALOIDs with "br" phonetics/@comment-24889894-20161214132105/@comment-6433273-20161215000422

I think that most of it can be due to CRYPTON, Internet Co., (and I think also AH-Software, I forget if miki, Yuki, and Iroha's V4 trials had it) recycling their older V2 voicebanks. This may also explain why CFM's Japanese VBs V3 & later have these samples but not the English ones. While I can't say for Miku and KAITO's English, MEIKO's, Rin & Len's, and even Luka's V4X English VBs don't have these functions. As for the other companies I'm not sure.