Yes I have bumped this topic. I reviewed over 70 search returned thread and this is the one best suited for the item I am showing, a 1879 J4 on cover usage. While there are many threads about the stamps off cover, especial the cover differences on the first issues, there was not general on cover usages topics except for a single specific value such as a 1/2 cent covers.
The EKU for J4, shade variety not specified, is July 7, 1879. This cover is dated within the first 7 weeks. While a nice example of a J4 usage the recipient is worthy to be on the internet as Captain A. (Andrew) J. Mosher has his letters and papers reposing in the library. During the time surrounding this cover, the Captain was stateside between several of his long whaling voyages. Later he handled ships not engaged in whaling.
While reduced on the left edge as viewed from the address side, it is likely no important information is missing such as a vertically written return name or address. If that was present the letter should have been held for postage from the sender.


The circle T marking, international for indicating postage due, plus the 10 cents collect seems to indicate the cover was presented unpaid from a non-US ship which would be rated as a UPU 5 cent letter with the amount due doubled as a penalty. UPU letter rate began 7-1-1875. With a full date in the NY due marking, one could even research the NY ship traffic record to see upon which ship it may have arrived.
I invite comments and corrections as this is not an area I in which I am strong. It is an area in which I would like to expand my knowledge.