A few objections.
First, I would object the general address of your considerations: the knife is not "unique", there is no "uniqueness" of the item actually, not even within the borders of this trial. I have the feeling that your adress of a "uniqueness" may an ideological rationalization meant as a prelude to justify the plan of putting aside, "not considering" the evidence.
In the merits:
1) it's incorrect. First, as for testimonies, the imprint was not considered the imprint left by a "small clasp knife", and second, the officers had been specifically briefed about that a wound appeared as if it was caused by a "large" knife (Finzi's testimony).
2) Sollecito's flat was searched on Nov.6 by my knowledge, that is basically the day of his detention.
3) According to Finzi, the knife was picked primarily because it appeared as potentially fitting the victim's wound, as it had been described to Finzi (he did not see the wound, was briefed about it).
4) the knife was repackaged, but: a) it was hardly exposed to contamination from Meredith's DNA, since Meredith's biological fluids had no reason for being present in the environment during re-pacakging; b) contrarily to your statement, there was a good reason to re-package the knife in a hard cardboard box, an obvious security reason, so that the blade could not poke through the envelope, to provide for security of the object and of the people who would handle it.
5) the "mark" appeared as a potentially useful element because it was a scratch on the metal, therefore had some chance of retaining cells despite cleaning. It was quite interesting also because it looked as if the knife had been energically cleaned with a scratching sponge.
6) IIRC the test was recorded correctly, but at preliminary hearing Stefanoni didn not remember correctly about having used Qbit fluorimeter alone on A,B,C rather than PCR quantification. Prof. Potenza anyway was there.
7) sample B anyway had a DNA content and that was extracted.
points 8 and 9 are questions and would be good points for a cross questioning, which is defence's work; this would have required prof. Potenza to document the work, in a way that it could bring that to the attention of defence lawyers. But Potenza failed to provide any type of observation on the point. He observed the work and didn't think these details were worth to be documented.