Crockford has said that people were using JSON before he "discovered" it. That's why he says he discovered rather than invented it.

Unfortunately I don't remember who those people were, but anyone who used XmlHttpRequest, which was apparently there in the 90's, could have used it.

I made up and used something similar to JSON in 1996. It's not difficult to think up if you're trying to find the simplest possible text-based hierarchical data format. There were a lot of variations on this idea.

Well, it's possible an object was transmitted as JavaScript source (to be decoded using eval) before the JSON spec existed.