Possible Plate Number Single- Questions??

I am still trying to learn all of the terminology of this hobby. first off, have I correctly identified this as a plate number single? Secondly, does this plate number add any significant value to this particular stamp? Thanks!

first off: yes secondly: no

Thanks!

There are, however, good plate numbers (clear up to the present) hiding out there, some of which are known only as singles, and/or known only as used. The Durland Catalog is the final authority on 99.99% of the rare numbers.

From a quick look at Durland for instance, you would find a 20c Presidential that catalogs over $3,000 (!), and even among the common 3c commems of the late 1940s, two of the Mount Palomar #966 plates catalog $1.25 and the other two catalog $2.50; there's unexpected value everywhere. And regarding the 21c Presidential, as a further example, there are two plate numbers worth 50+ times the common numbers, and interestingly enough, they are known only precancelled.

Never tear off the selvege if it has the plate number on it.