I can find episode 1 in a few places on iOS with it showing the aired date but it still gives a subscription error regardless. I imagine it'll be listed somewhere on Android with the aired date but still give an error too.
You'd think Sky are doing it as a benefit for box sets customers as in people without a box sets have to wait each week to record or download the catch up, which would be a fair thing to do, and box sets customers can download them all.
But that is not how they behave on the boxes so seems a bit strange to make them behave that way on the apps.
And even when they are catch up, it's a right pain to get them to work on some devices.