["?"]

Actually there would be no obviousness in the usage since both types can use it fairly well, neither function focuses on the present and both ITJs show the world only their extraverted function (Te). I am not sure why how one would know whether they're observing any introverted function since it is just that introverted.

On the other hand you may be able to make a distinction through their core temperament needs. I would say that ISTJs like all SJs, will be civic minded. I think that ISTJs are probably more prone to being mistyped as extraverts because they can be community and group active.