D&T's first ed. was reviewed in "The Graphic" (London) on Sept. 9, 1887, in the column headed "New Music."

The 1887 date is also that given by the British Library, so between the two it should probably be taken as authoritative.

The National Maritime Museum in Greenwich dates their copy of the 3rd Ed. to "ca1890."

D&T Mystery solved! (Thank God!) James J. Fuld's "Book of World-Famous Music," 5th ed. (N.Y.: Dover, 2000), p. 206, cites a letter from Boosey & Hawkes informing him that D&T's 2nd ed. was published Feb. 17, 1890, and was "withdrawn Feb. 18, 1890, for a reason not now known." The 3rd ed. was published "in 1891."

SO, FINALLY: D&T ed. 1: Mid-1887.
                ed. 2: Feb. 1890.
                ed. 3: 1891.

The acknowledgement to L. A. Smith in ed. 3 may be a clue as to why ed. 2 disappeared so quickly: D&T may have reprinted something before obtaining her publisher's permission.