You're on the hook for whatever counts you were charged with in whatever charging document you faced when you plead. If you plead to one of the 10 in the information (the post-preliminary hearing charging document) and the remaining counts were dismissed with a Harvey waiver, you're only responsible for the restitution as to the 10 counts, not the 50. Those other 40 counts were dismissed.
A Harvey Waiver refers to the 1979 case of California v. Harvey. The ruling in that case was that a court cannot consider dismissed charges in determining the amount of restitution. If you waived the right to keep the dismissed charges out of 'the calculation.' Then the court can consider the charges that you were charged with before you changed your plea.
If your co-defendant was charged with counts that you were not charged with, then those counts cannot be considered against you for restitution.
If a preliminary hearing was conducted and you were not held to answer on some of the charges then a strong argument could be made that those counts should not be considered as well.