Marshal, In NY with our pistol permits we also have a second card that includes information on any handgun we are licensed to carry. It lists Manufacturer, Model, Caliber, and Serial Number and they are the only guns you are licensed to carry.
I just today added a new (to me) Bisley to my license. In order to add it i had to take a receipt to the county clerk and file an amendment to have them add it, then go back to my FFL for him to run a background before it would transfer to me.
To remove a gun from my permit I have basically 3 options - show it was sold/transferred with a receipt or report it as lost/stolen with a police report. My guess is that is why he is asking you - I would have assumed the Gunbroker traffic would have worked but I haven't sold anything...
This link is the amendment for my county just as an FYI. https://web.co.wayne.ny.us/wp-conten...4/12/PPB-5.pdf