By century[]
Unknown era[]
Aenar sighters []
According to Thy'lek Shran, only a handful of Andorians had ever seen an Aenar face-to-face as of 2154. (ENT: "The Aenar")
These Andorians were only mentioned in dialogue.
Although the existence of Aenar was confirmed in 2104, they were believed to be a myth prior to that. Shran may only be speaking of those who had seen them in the 22nd century, or including those whose tales led to the myths.
Renegades []
These renegades, while in the Triangulum system, dismantled their ship and hid it, leading a Starfleet admiral to believe they had left the system.
Jean-Luc Picard recalled this incident when Worf failed to find the hostiles that had attacked the Delta Rana star system in 2366. (TNG: "The Survivors")
These renegades were only mentioned in dialogue.