There has been a short email discussion about how to indicate information not found on a map, and how one indicates that a title has been supplied by the cataloger.
According to RDA 2.2.4,
When instructions specify transcription, indicate that the information is supplied from a source outside the resource itself:
by means of a note (see 2.17)
or
by some other means (e.g., through coding or the use of square brackets).
However, 2.3.2.11 says,
"if the resource is a type that would normally have identifying information (e.g., a published book), make a note to indicate that the title has been devised." Mark Ehlert says, "Taking the aforementioned "or" into account along with the quote above, brackets get pushed aside for made-up titles."
Also refer to 2.3.2.11.2 which refines the made-up title instructions for cartographic resources.