=== In reply to your comment, Fran
/che si fosse/ is the subjunctive mood, past tense, which is appropriate
in this context that is expressing a possibility of a past event.
Subjunctive mood is not an easy subjecvt, not even for Italian mother tongue speakers.
It is needed under certain semantics like:
a) possibility
b) wish
The story is quite long and (I think) should be addressed
examining examples you would like to propose, one at a time.