If the parts are being replaced on a warranty claim, then yes Harley does require the dealer to return the old parts and they do have the right to require you to surrender those parts. However, if the parts are being replaced as part of an insurance claim, Harley has no legal claim to the old parts. The insurance company can keep old parts they pay to have replaced and then sell them for salvage value to offset some of the repair costs. If a dealer is trying to tell you you must give them the old parts on an insurance claim, check with the insurance company and make sure they aren't really the ones pulling the strings. If they will release the parts to you, the dealer has no legal claim to those parts. Some places will play the game and sell the old parts for additional profit. A dented or scratched part that has to be replaced rather than field repaired thanks to Harley's restrictions on the paint for a CVO can still be repaired and painted a standard color and sold to anyone who wants it. Extra profits for the dealer, using your old parts they obtained for free. Don't fall for it.
It is best to get this all sorted out beforehand with the insurance company and the dealer, and if any particular dealer wants to play games you need to go to a more ethical establishment before ordering any parts.
Jerry