As for the 1st paragraph, I'm afraid I am not following you.
The list that I have made portrays a summary picture of the current status of what the trial findigns are and judicial truth.
From a legal point of view, this legally constitutes a framework, a basis on which any possible action may occur.
The legal framework also is considered as a sort of acknowledgment about findings and proceedings. It may be seen as something that expresses and points to a historical truth.
The second calunnia trial is absolutely not a waste of time: it will come to a conclusion, and will bring to a judicial truth. There are some probabilities that time is not enough to sort penalty effect (albeit the expiration time is more than 11 years on aggravated calunnia of this kind) but even without prison penalty there is a finding and acknowledgement of judicial truth.
As for Guede's trial, it shall be clear that in the Italian system trials are not entirely independant from each other. A conflict of res iudicata is normally regarded as unacceptable, meaning that truths established are important and have some consequence universally, not just within a limited boundary areound the parties of a trial.
Guede's trial leads to a judicial truth which everyone can hold as evidence, even in legal venues. (it is not true that Knox defence was not represented in that trial btw, but that's not the point).The fact that Guede was not holding the murder weapon is thus a definitive finding, something that allows to people say and write things and may allow lawyers and judiciaries many kind of things.