I do not know what state you are from but will assume they all have some similiar laws like the ones here in California to protect you. If you want the old parts back, you must ask for them before any work is started. The shop is required by law to return the parts to you only if you have requested them before the work is done. So if you are asking for them after the work is done, most likely the part was already tossed? Also if there is a core charge on a particular part, if you want it back you will need to pay the shop for the core.