The conventional wisdom among booksellers is first edition Dr. Seuss
books cannot be identified without the dust jacket. This used to be
true. With the recent discovery of some salient information, today,
most of the large format Dr. Seuss books can be identified as first
printings without the dust jacket.
To see points-of-issue, with photographs, see:
http://1stedition.net/blog/2007/05/dr_seuss_first_edition_books.html