A few things here. One your dealer did the work that is on your invoice. This is a recall. If the dealer lied and didnt install said parts, said parts failed, especially a recall part, the dealer would get shut down in a heartbeat for insurance fraud and other reasons! I dont think they would want that problem, especially since its such and easy replacement. Most dealers I know of do not put the stickers on even when they replace a part. If BMW put stickers on for every warranty/recall part your car would look like a College football helmet with all the stickers!
Plus if the dealer forged an RO said they replaced parts and didnt, they still need to send the parts back to the manufacturer. So if they didnt do the repair, where would the parts come from to send back? No, you cannot get your old parts. They need to be sent back to the manufacturer. All warranty claims are like this. If you paid out of pocket (assuming there is no core charge) then you can request the old parts. In your situation this is not the case.
The parts replaced will be on your invoice, that will tell you if they replaced the injectors(all or some), HPFP and reprogrammed. Also if you want to check to see if the HPFP was changed. From under the hood, shine a light down on the driver side of the block and look at the pump. If it was replaced, it will clearly be a brand new looking part. As far as the injectors, if you are really curious, pop off the upper engine cover and look at the injector part #s.
I highly highly highly doubt the dealer said they did the repair, but really didnt.
btw- its beCAUSE