You do not need to hand over the Cisco Serial Numbers for Licensing purchase from Cisco or a Cisco Reseller.
This would be in the case that this reseller, manages all licensing handed over to their customers - such as yourself. This is not standard practice.
The business I work for performing licenses like this: we would purchase based on Part Number, allocate the Licensing to the point of contact - who would then then Activate the PAKs into activation-keys for each device.
This is performed on the Cisco Licensing Portal:
https://slexui.cloudapps.cisco.com/SWIFT/LicensingUI/Quickstart
Kind Regards, Frank Ralston