Do the Coda books have to be read in order?  Not necessarily.  You can start with any couple, but I’d recommend reading each couple’s stories in order.

Did that even make sense?

You should read Promises before you read the short story The Promise or Putting Out Fires. And you should definitely read A to Z before The Letter Z and/or Paris A to Z. But you can read A to Z without reading Promises first, although you’ll probably enjoy the last half of the book more if you already know who Matt and Jared are. And Strawberries for Dessert is only tangentially connected to the other two and can definitely be read on its own.

If you really want to read them in order, then go in the order they were written, which is:

1. Promises
2. A to Z
3. The Promise and The Letter Z (doesn’t matter which one you read first – they take place at the same time)
4. Strawberries for Dessert and Putting Out Fires (also take place at the same time)
5. Paris A to Z

For details about the exact timeline, see here.

One More Soldier, Between Sinners and Saints, Song of Oestend, Blind Space, and Cinder are in no way connected to any of the previous stories (or to each other) and stand completely on their own.

The Scooby story is more of a joke than anything. If you haven’t read the Coda books, you probably won’t find it funny. Even if you have read them, you might not find it funny.

Breakdown, in order, by couple:

Matt and Jared:

1. Promises
2. The Promise
3. Putting Out Fires

Zach and Angelo:

1. A to Z
2. The Letter Z
3. Paris A to Z

Cole and Jon:

1. Strawberries for Dessert
2. ???

I hope that cleared it up, and didn’t just create more confusion.  :-)