It is the no watermark issue, currently the plate is unknown to me, I am in the process of writing a book on the 1938-1966 half-penny kangaroo, it's errors and varieties, hopefully I'll find the plate during my research if it is possible.
I know, they had a half-sheet and separated them into various blocks, if you look on the website you will notice they have a block of 16 as well that is identical. I buy all my stamps from the Juzwins. Some are identical, others are not.
I bought some very valuable items from them, and every possible variety of the half-penny kangaroo (1938-1966) so I can add them to a book I am currently writing in relation to the issues and varieties of this particular stamp, many in complete progressive states.
I have over 4,000 of these stamps that belonged to a project that took the authors of an earlier book (incomplete) over 50 years to complete, I intend to complete the task with the equipment I have that did not exist back in the 50s and 60s, I won't be infringing on any copyright issues as I own the rights to the copyright.
The equipment to finish the project is a special microscope, various illuminated magnifying glasses, specific software and a large 32 inch monitor to enlarge the images to see the variety in detail.
I bought that project from the Juzwins as well, I won't buy from anyone else.