> "Do you have the capability to retrieve this PIN number?"

The answer to this question is no, since the person would be no longer employed by Apple, would not possess the source code, and would not possess the signing key.

Even if you assumed that the court could force Apple to disclose these items to somebody who is now a third-party, it may be the case that there isn't any person who is capable of doing this. Are the same people at Apple responsible for code signing and writing the code necessary to do this?