Auto-renewable In App Purchases (aka Subscriptions)
Readers that subscribe to your magazine will receive the current published issue free, as well as any future issue published during the cycle of their monthly, bi-monthly or yearly subscription (depending on duration set for subscription).
Non-consumable In App Purchases
A Non-consumable In App Purchase enables readers to purchase single issues of your magazine. Each individual Paid issue must have a Non-consumable In App Purchase setup and submitted for review.
If a reader subscribes and issues were published before they became a subscriber, then they will need to buy those issues.
Any Special issues published will need to be purchased by both subscribers and non-subscribers.
If the issue is Free, than anybody can get access to the issue.
Subscribers Only Issues
If the issue is Subscribers Only and marked with a Private sash, then only subscribers can get access to this issue and if you have subscribed today, but 4 months ago an issue was marked as Subscribers Only, then you will get access to that issue.
Subscribers Only back issues work differently from standard Back issues in the sense that a new subscriber will be able to get access to all Subscriber Only issues, past, present and future.