Some images from old cartridges not searchable in Design Space, so if you don't have a record of what you have, you might not even know where to look.
So I got my Paper Dolls Dress-Up cartridge linked, which they had to do manually, since I bought my Explore second-hand and Cricut refuses to transfer their record of ownership to me. (I think they think I stole it.)
I was glad to finally get that linked because the cartridge has a host of fun, if "cartooney" content, including a pirate ship, the Mayflower, several dinosaurs, three castles, two ships, and countless little detail items.
But when I search for "dinosaur" or "castle" or "ship" in my image sets, these do not show up. ( I tried "dino" and "boat," too, in case you wondered.)
When I go to the Paper Dolls Dress-Up Image set, the images are all right there. But if I wasn't already familiar with the cartridge, I wouldn't have known to look for them.
I have no idea how many other images I've used over the years that aren't indexed, either. A random spot check shows several more cartridges that aren't indexed as well.
The truth is, I don't really use my cartridges all that much, but if I'm looking for, say, a castle pattern, and I have five or six on different cartridges, but none of them are indexed in Design Space, it's probably a good idea to keep my booklets available.