I have a question for you. I bet it is something you have noticed many times, but never paid attention to it.
Scott #771 is the imperforate 16¢ Airmail Special Delivery issue from the Farley special printings. It’s regularly issued perforated cousin is Scott #CE1.
If the regular issue is in the Airmail Special Delivery section of the Scott US Specialized catalog, then why is the imperforate version listed in the regular issue postage stamps section? It is after all, clearly an airmail special delivery stamp.
The obvious answer is that catalog editors of yesteryear grouped all of the Farley Special Printings into a consecutive group of catalog numbers. The #771 issue was the only special printing that was otherwise not an ordinary postage stamp.
The Farley special printings, Scott #752 thru #771, all have major catalog numbers. Having a major catalog number assigned means that issue is more likely to be collected.
When the USPS decided to sell the modern uncut press sheets, Scott catalog editors initially decided not to list them. That decision was later changed and they are now listed with a minor letter designation under the normally issued copies with die cuts. These are special printings too. So why do the Farley printings have major catalog numbers and the uncut press sheets are a minor letter?
Have you noticed that there is no Scott catalog numbers 779, 780, and 781? That is because the TIPEX souvenir sheet (#778) was imperforate and had four different designs. It was initially listed as catalog numbers 778-782. Later, the editors changed their mind and used #778 as the only catalog number. Rather than reshuffling the other catalog numbers (leading to endless confusion), the catalog editors just abandoned use of the now three unused catalog numbers.
Check out the catalog for Scott #1288. Did you ever notice that there is a Type II of this stamp, Scott #1288a? The difference is whether the tie touches the jacket or not.
Compare that to the 1¢ blue Franklin issue, Scott #5 through #9 for the imperforate issues. The differences between different types of this stamp are equally as trivial. Part of the design is cut away here, a line was recut there, something broken over here.
The 1¢ Franklin warrants major catalog numbers for tiny design changes. Yet, the design change for #1288 is merely a minor catalog number.
The Scott catalogs have been around for over 100 years. Editors have come and gone. Decisions have been changed over time.
There are other little quirks and inconsistencies in the way the Scott catalog lists stamps. I think an interesting and not terribly expensive collection that will take a lot of investigation and a lot of fun would be to form a collection of these quirks and inconsistencies.