If I was requested to do the same by one of my customers, I would retain samples to protect myself (& my company), so if there were any questions or accusations down the line, I would have samples to prove what we had made and what material had been used.
I had a case around 4 years ago where an automotive customer accused us of initially using an incorrect grade of material on a product, 5 years previously. The automotive company were threatening millions of euros fines for field failures and a product recall which we would have to fund, so I sent the PPAP samples from that initial batch and the FAIR samples from the other batches produced that year to an independent company for testing and the results were that they had all been made from the correct material, so I submitted this information to our customer.
The automotive company must have looked for someone else to blame, as they never mentioned it again.