So I've had time to take a look at the code again, and it turns out the API actually returns bookable=true for those flights as well. In fact, there is no difference in the response between those flights and the actually bookable T+353 flights, so I have no way of telling them apart in the code. I don't think there's anything I can do on the script end short of just hardcoding it to ignore flights after 353 days, but on the other hand, it seems it might be handy to be able to see in advance seats that might open up in the next week. I'll probably add a message somewhere to alert the user that those flights may not be bookable yet.