although I think the act of taking thr tests repeatedly would tend to increase introspection, in the manner of observation effecting the outcome

It may also just increase the "ability" of taking the test such that it produces outcomes that match better with your (desired) self-perspective. I've noticed a slight drift from INTP to INFP (which I identify with a bit more) in repeated self-administrations of the test. Possibly that's just due to how I feel on a particular day, but partly I may be choosing answers which favor F over T without outright lying in cases where I am not very sure.