I made my application online 9 May 2022 posted old passport special delivery to be signed for to CORBY. It arrived but the person signing for delivery did not want to be known it looked like art painting on the pyramids so whether that would stack up in a court of law who knows?
I did however email them to let them know that i knew they had received it but its as someone else has said no one is bothered to scan them in therefore there is probably a big pile stuck somewhere.