non renewable expiration date

For non-renewable subscriptions, the duration is not managed by Apple/StoreKit. You'll need to manually calculate it yourself by your own means (e.g. tying a product sku to a duration you define via a configuration/database on your own server and add that duration length to the purchase time in the receipt).

Thanks a lot but,

I can't see a difference between this and a "non consumable item".

I mean, let's say we define an in-app non renewable subscription for the italian football 2017/18 season. What my client want is to let it up till the end of the season. Isn't the same as to define a non consumable item named "italian football 2017/18 season", as from my point of view our code needs to handle the expiration in both cases.

You're correct in that they're very similar conceptually. The difference being that you can purchase a non-renewable subscription multiple times whereas a non-consumable can only be purchased once. The purchase also remains in the receipt indefinitely so it's not quite like a consumable either. There's a good comparison of the differences here: https://developer.apple.com/library/content/documentation/NetworkingInternet/Conceptual/StoreKitGuide/Chapters/Products.html#//apple_ref/doc/uid/TP40008267-CH2-SW4.

A non-consumable cannot expire at a set time. A non-renewing subscription can expire at a set time. If you are making information regarding a particular season available for all time, you can choose to implement a non-consumable for every year. Or you can implement a single non-renewing subscription and make it cover the year in which it was purchased. The receipt will show the purchase date so determining the expiration date is not that hard.