Are you sure that it is vitamin B1 that is working? Are you completely fluent. I guess there is nothing like 90% fluent and 10% stutterer. Person who don't stutter, there is nothing like that. If B1 would have really been working, you would have been as fluent as normal people are It might be placebo. Because stutters have good days and bad days and I myself consider that I am 90% fluent now a days but sometimes I perform bad at speaking.