A Misstep between the Towers?

If you are a collector of Caldecott first editions, grab your copy of Mordicai Gerstein's THE MAN WHO WALKED BETWEEN THE TOWERS. Does the information on the bottom of your copyright page look EXACTLY like this?



If so, congratulations -- you have a true first edition!

However, I have come across some copies of the book that have confused me. They are the trade edition, with the correct ISBN number, yet the information on the verso reads:

ISBN 0-7613-1791-0 (trade edition)

1 3 5 7 9 10 8 6 4 2

ISBN 0-7613-2868-8 (library edition)

3 5 7 9 10 8 6 4 2

This information indicates that the trade edition is a true first printing, while the library edition is now in its second printing. But how is it possible for a first printing of the TRADE EDITION to have any kind of number changed on the copyright page and still remain a first printing? When the printer stopped the press and removed that number "1" from the second row, wouldn't the rest of the books in that print run by considered second printings? If not, then that means not every first printing of this book is identical; some have the complete number runs listed, while others have a variation in those numbers.

Once again, I'm confused.