Point this out to your attorney. If they have lost a portion of the report then they may not establish the factual basis for the stop, detention and arrest. If it is just a faxing or filing error they will get you the correct report.
If there are errors in your police report (and information about someone else's arrest would be an error), then you can attack the police report as an untrustworthy document, and build defenses from there. You should speak to an attorney in your area in more detail about your case.