CRRR = Certified Return Receipt Requested. When the post office delivers it, someone at the court MUST sign a receipt. The post office will send that receipt to you. THAT is your proof of service. Whether of not it actually makes it into the file is inconsequential -- you have proof that you "filed" it with the court.

Yes, someone else can deliver it to the court. Just make sure they take two copies and have them both stamped. The clerk keeps one, and your friend can send the other copy back to you. Your copy will then have stamps from BOTH the prosecutor AND the Court. This is the safest way to show "proof of service".

Barry