Hi ScottZ --
Welcome to the forum -- and I will say that having collected and specialized in the 1851 3-cent issue for many years -- that dudley did a very nice job of explaining and summarizing the differences in how to classify the stamp by Scott #.
You made reference in your original post to a presentation by Don Getzin -- which I had not seen before -- but just took a look now -- and I think Don did a great job of illustrating the differences as well. Link to Don's presentation for others who may not have seen it is here:
http://hamiltonphilatelic.org/prese...mpressed.pdfThere are other resources you can look at as well, including -- as dudley mentioned -- the Scott US Specialized catalogue.
Also, there is an "Easy ID" article for the 3c 1851 stamp on the StampSmarter website -- link is here:
https://stampsmarter.org/features/S...Plating.htmlIn any event, after all the dust settles and all the smoke clears -- the definition of the various Scott numbers for the 3-cent imperforate issue of 1851 boils down to two factors --
-- First -- the plate from which the stamp was printed
-- Second -- the presence -- or absence -- of recut inner lines.
Note that the color of the stamp is NOT a factor in determining the Scott catalog number.
Consequently, as dudley noted, the only 100% sure way to determine the Scott catalog number is to plate the stamp -- or at least be able to determine the plate from which the stamp was printed.
If you have not yet checked out StampPlating.com -- there is a tab that summarizes how to ID the various plates -- and a ton of other information about the stamp as well. Link is here:
http://stampplating.com/identify-platesAs an aside -- The plates that printed the #10 and 10A stamps were in use for only a very short time -- and the number of stamps printed from these plates pales in comparison to the plates that printed the #11 and #11A stamps -- which, generally speaking, drives the significant difference in Scott catalog value.
Again -- welcome to the forum.
Regards // ioagoa