Thanks guys! I used to have them in a ring binder but of course that means making big holes in them!
Coptic binding means I can open the book flat to see the outside or inside of each card fully.
I didn't trim them, I aligned them among the bottom edges and then just did looser stitches higher up if I needed to account for a small card (umm... I've explained that badly! I'll see if I can add a pic!). You could also organise them by size, but I wanted to keep them chronological - and that way I can also easily add more to the back in the future