I am done with SimplyMac. They are either incompetent or overloaded with demand. Either way they refuse to accept responsibility for the mistakes they made, which incidentally I can easily prove. I have not altered the disk that SimplyMac installed El Capitan on with the incorrect filesystem case sensitivity except to create an account.
I have discovered the issue causing "This Apple ID has not yet been used in the App store.". This is simply a case of undisclosed info and requirements. Apple has done a very poor job on documenting the requirements for using recovery mode.
For the multitude of others suffering from this problem I'll review what is required.
1) You must have or create an AppleID and tie a payment method to it using a credit card for example. That is what I did, but that's not enough. There may be other payment options that will also work. There are several ways to create the AppleID if you don't have one. I had no difficulty in finding info on how to do this.
2) There may be other methods, but what worked for me was to boot OSX normally and open iTunes. Sign in with your AppleID. You may get a similar error, "This Apple ID has not yet been used with iTunes." Now however the "Review" button will work, unlike in recovery mode. If you get this message click the Review button and make sure everything is correct. Once you do you will see the "You may now use this AppleID to make purchases from iTunes or the Apple App Store." or something like that. In my case the 3 digit security code was not correct, and I didn't have a Mr. | Mrs. etc "title". Those issues SHOULD have been caught by the "Manage your AppleID" website but guess what, IT DOESN'T!!!
3) Now that the iTunes store has blessed your AppleID you can now restart the system in recovery mode by holding the Option key + R. When you're prompted for your AppleID you will not see the "Haven't used" message.
Now however, I hit a new roadblock: "The item you requested is temporarily unavailable." I suspect this too is a BOGUS error message, and the message should instead be: "The version of OSX you requested is no longer available. Would you like to upgrade to the latest version?" I am speculating here (Apple forces us to do that alot), as an older OS may be available for download but "temporarily unavailable" due to overloaded servers that can't keep up with demand.
I will also warn you that once you get this message and cancel that dialog, any further attempt at clicking the "Install" button will briefly show a progress popup saying "Signing into the App Store", but then NOTHING - no error message or clue to the user as to what is going on. Not even a repeat of the "temporarily unavailable" message. This too is a BUG, or in the very least poor design.
I have another external drive I have installed Sierra on, so I will attempt to recover a Sierra OSX and see if I get the same message or if the "temporarily unavailable" message continues to be the response. If that is the case I will wait until late tonight to try this again, going back to El Capitan.
I hope this detailed info will help others. I'm not holding my breath for Apple to fix their docs or bugs on this issue.
The process of recovering the OS should NOT be this difficult, nor should info on how to do it correctly be so hard to locate !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!