First of all: "tell me again" is a rude request. I am not supposed to tell things twice.
Second, Guede was not carrying a knife. He had a knife in his rucksack, and the bag was inside a building. There is no crime in this. Carrying a knife means carrying on your person or in a vehicle from a location to another.
Anyway I made a mistake: because, re-reading the article. I thin the unjustified carrying of a knife refers to the carrying of the kitchen knife back from the cottage to the apartment.
Last, not only Guede could not be charged or prosecuted, but also the main point is that a prosecution on those alleged charges would have been irrelevant, because it could not be used in the Kercher case. The Milan episode obviously could not be prosecuted by Mignini because Milan is a different jurisdiction. He was caught with stolen items in Milan: this means only a Milan proseutor could deal with this.
But also, most important, you are talking about charges related to other deeds totally independent from the Kercher murder, therefore they cannot have an influence in the case. If Guede already had established criminal records, then those criminal records could be used, but only to argue against mitigation, not to increase the penalty (anyway Mignini and Comodi already managed to obtain the highest penalty, that was 30 years, they could not obtain more on that charges).
But Guede did not have any criminal record. Above all, he had no criminal record for rape and violence. Also, no theft was proven to be committed in the house; not even drawers were searched.