I think that it to have a lockout (by unscrewing the tail cap, the threads at the end of the battery tube would have to be anodized (and the end edge would not be anodized). Is that the case with this light? The way that would work is that by anodizing the threads and leaving the eddge unanodized, when you screw the tailcap on tight it makes contact with the exposed edge.
EDIT: The 2nd and 4th pic in the OP in this thread:
shows (I think) how the lockout would look (at the end of the battery tube).