"Option A: Read authors A to Z. Commit to reading 26 books theoretically speaking.
Option B: Read titles A to Z. Commit to reading 26 books theoretically speaking.
Option C: Read both authors A to Z and titles A to Z (52 books; this is the challenge Joy created)
Option D: Read internationally A to Z (books representing 26 different countries) (The books could be from international authors (writers from that country); however, it's fine if a book is only set in that country. If need be, instead of countries one could use cities, states, regions, etc. The idea is to use proper place names. If you'd like you could even use a few fictional countries.)
Option E: Read 26 Alphabet books. Embrace your inner child and go visit the children's section!
How strict is the 26 or 52? I know it isn't always easy to find those difficult letters. The thought of finding the X's (for example) might scare folks away. It shouldn't! I'm a merciful host! (Ask anyone!)
If you want to give the X's a go... For authors, try to find an X in the first name, middle name, or last name. For titles, it doesn't have to be the starting word. Try to find an X somewhere in a title, and it'd count in my book.
Still can't find a book for the letter you need? I'll take your word for it. I've been there. I know. If your library doesn't see the need to order books just because it starts with an X, then I don't blame you for not wanting to special order a book that you may or may not enjoy. You gave it your best, don't feel bad. You can still make this challenge work for you.
Don't be afraid to ask for recommendations. Look at the previous site. Ask other participants. Or ask me, your host. I may not have the "right" recommendation for every letter, but working together, I bet you'll find something that interests you.
Audio books count in my opinion. If you take the time to listen to books, then that should count towards something.
What about rereads? I don't have a problem with rereads. I would hope that you'd want to mix it up a bit and read some new authors, new titles, etc. But I'm not going to require that by any means.
What about children's books? Children's books and YA books count along with adult fiction and nonfiction of all sorts. (Poetry and plays too. Short stories count if they're in a collection.) I don't see a need to discriminate between "adult" and "kiddie" books. Even picture books can count if you like. Though try to use them in moderation. I used a few picture books to get tricky letters this year."