Is cis or trans identity really something that is truth-apt (& therefore in the purview of probability)? It seems to be a combination of self-description of feelings, plus chosen group affiliation.
The self-description of feelings is presumably more or less infallible, and the group affiliation is stipulated by the individual.
Well, it's possible to be wrong about your own feelings. The question that matters is "later, after transitioning, would I feel better or worse than I do now", which isn't necessarily infallibly correlated to your current feelings.
Rationality quotes time!
The usual rules: