A trip over to Amazon.com proved fruitful! The answer to your original question seems to be yes. On May 9, "Behind That Curtain" was released, thus indicating that the rest of the stories will be available at some point fairly soon.
For those not familiar with the current releases of the Earl Derr Biggers Charlie Chan stories, I can tell you that these are of fine quality, and each has a very handsome cover (dust jacket) illustration.