1st Dr. Jekyll ?

I have two copies of Strange Case of Dr. Jekyll and Mr. Hyde by RL
Stevenson, 1886. Both copies match all aspects of the first American
edition in boards. Both copies are identitical except in one respect ...
size. One copy is approx. 1/4" - 3/8" larger, taller and wider. Beinecke
edition is listed as 7 3/8" x 4 7/8". (a second question is -- are these
measurements for the boards or the pages?) Neither of my copies match these
dimensions exactly. The smaller book is 7" x 4 1/2". The larger is close
to the Beinecke figures. Is it normal that in binding the books, sizes may
differ by this much? The text appears to be the same, but the margins are
different. Any confirmation of this situtuation would be appreciated.
Thanks, Jeff