NCC-1831 was the registry number of a Federation starship which underwent a layover at Starbase 11 in 2267. The ship's number was seen on a chart indicating the repair status of several vessels. (TOS: "Court Martial")
This ship was only identified by its hull number, and only when the remastered version of "Court Martial" became available in 2008, was the registry clearly legible.
And indeed, when Greg Jein embarked on his influential 1973 "The Case of Jonathan Doe Starship"-article, he had misread the number, which he had assigned to the Constitution-class USS Intrepid, as "1631", unsurprisingly perhaps, as he had to make do with a low-resolution still (given to him by future Star Trek reference author, but fan at the time, Kay Anderson) from the already low-resolution original series run.  As later friend and co-worker Michael Okuda had access to an early 1990s remastered version of the episode at that particular point in time, he corrected this number in his registry list, otherwise largely based on Jein's, in his first 1994 edition of the Star Trek Encyclopedia (p. 320, ship list) to "1831" – though he had overlooked to change the individual entry for Intrepid accordingly. Yet, Okuda re-corrected himself in the third 1999 edition and had the original "1631" intent subsequently applied on the retconned Intrepid in the 2006-2008 remastered version of the Original Series. It was exactly for this reason why Matt Jefferies had avoided the numbers 6 and 8 when he devised the original registry number for Enterprise NCC-1701 in 1964. (Star Trek: The Original Series Sketchbook, p. 62)
Confusingly however, the later USS Enterprise Owners' Workshop Manual (p. 38), on which Okuda had served as technical consultant, adhered to his first edition Encyclopedia interpretation of NCC-1831 being the registry of the Intrepid, but in canon, "NCC-1831" has become orphaned.