NSW Overprint "Specimen"

I need your help to identify this stamp from NSW with overprint "Specimen"... I can't locate it in my catalogues.

Looks like Scott # 81.

Thanks for the help, but I'm really looking for the catalog number with the overprint...

Catalogues often don't assign a number to specimen stamps - there's often simply a note beneath the standard set with a price.

You won't find this one in the catalogues Murasama

This one was issued for collectors here in New South Wales in January 1893. There were only 240 done (ie: one sheet).

Thanks for all your help!!! I am very happy with the information and the stamp!! It's a great addition to my simple NSW collection!!! I was able to find the small note about "Specimen" in the SG Commonwealth catalogue, but it does not offer information as interesting and extensive as the one you provided me. Very grateful!! I also found a specimen to compare in Delcampe, which has also given me an orientation of the value since in the catalog they make an estimate for the entire group of Specimens of the issue.