Numbers I have provided evidence of the kids' defenses putting forward expert testimony in what amounted to Rudi's trial.
The kids' defenses were allowed to make their claims in the preliminary hearing which apparently was/became Rudi's trial. Both the PG and the PI wiki have the MR from Micheli.
There is a misunderstanding, as far as I can tell. Guede's preliminary hearing was the basis of evidence for his fast-track trial, which was held in closed session - that is, it was not open to the public and no details are disclosed outside of the motivation report. In a sense, a fast-track trial is a secret (closed) trial as long as the accused does not request that it be open.
This is not what is meant by representation, which includes the ability to challenge witnesses. Knox and Sollecito did not have standing, and thus would not have representation, at the Guede fast-track trial. Documents prepared by the Knox or Sollecito defense for other hearings, such as the preliminary hearing, may have been included in the dossier given to the judge. That is not equivalent to representation as understood in adversarial trials.