Where did you get the book from?
Only first edition is hard cover, soft cover is also first edition and all editions later.
Current listing seems a bit pricey for the book but it is getting harder to find. eBay
item number: 254776642259
At Abe's books pricing is normal: https://www.abebooks.com/book-searc...mar-william/
[EDIT: I though the link would take you directly to the search results alas, it does not. You are taken to the search box where you need to enter "Postal Markings of United States Expositions" and then search. Currently it returns three items, all 1st edition with one hardback. Two at $25, $4 S&H, from the USA and one at $35.74, $16.38 S&H from the UK. I list it for those closer to the UK.
DO NOT BELIEVE THE HARD COVER PRICING ON Amazon
!!!!! My hard copy ran $25.56 with tax and shipping earlier this month, a first edition hardback on eBay
. My later edition paperback is packed for moving. Easier to buy a new one for now so I got a hardback.