If anyone is concerned about an item offered being from the NYPL, I suggest they contact the library. When I saw an item on ebay with suspect provenance, I contacted the library and they indicated that it had indeed been properly deaccessioned (surprised they would have done that, but that's what the NYPL said).
The person who responded in 2008 was
Robert J. Vanni
Vice President, General Counsel and Secretary
The New York Public Library, Astor, Lenox and Tilden Foundations
Fifth Avenue and 42nd Street
New York, New York 10018-2788
tel. (212) 930-0744
fax (212) 391-2503
rvanni@nypl.org
Don't know if he's still there but he indicated the library welcomed such queries.
Max