I post the following response to my last statement from Ed Folsom,

William Sloane Kennedy in REMINISCENCES (p. 26) offers this very
straightforward list of attendees: "James Russell Lowell, John
Burroughs, and Professor Charles Eliot Norton, occupied the box at
the poet's right.  Mr. E. C. Stedman and his family were seated in
the opposite box.  Others present were Samuel L. Clemens, H. C.
Bunner, Frank Stockton, Moncure D. Conway, Joel Benton, Colonel John
Hay, Edward Eggleston, Andrew Carnegie, Augustus St. Gaudens, Mrs.
Frances Hodgson Burnett, Richard Watson Gilder, Mrs. Mary Mapes
Dodge, President Gilman of Johns Hopkins' University, Professor James
A. Harrison, Mrs. M. G. Van Rensselaer, and Miss Jeanette Gilder."
Kennedy is generally a reliable source, and the fact that he mentions
Clemens first in his list suggests the importance he placed on his
attendance at the event.

The NY Times account lists some of these people, but not nearly all of
them. It's a much briefer list.  Just the day before, they had devoted space
Clemens in their long account of the festivities surrounding Daly's
production of Taming of the Shrew.  So, on the one hand, it's odd they
wouldn't have mentioned Clemens in the Whitman account; on the other, their
society editor may have decided to spread the attention around by mentioning
some different names.