EBAE does not have any reference to this.
You can find it in Braille Formats: Rule 1 sect. 16.a
Although not an "official" reference the Literary Lesson Manual: Sect. 2.3 - first paragraph.
You may also want to reference the disclaimer in the 2007 Updates page F2: "... EBAE will have the responsibility for the formation and use of signs, symbols, and indicators. BF will have the responsibility of assigning print-to-braille formats ..."
I hope this helps