I believe you are misunderstanding the created_at field in the subscription objects. When someone resubscribes it’s still the same subscription, the date on the created_at field wont change under normal circumstances.
So for example, if a user called foo is a brand new sub, it will create a new entry for them, but if a user called bar resubscribed at the same tier they were previously, then nothing changes as their subscription object remains the same.
This endpoint is not intended to be a list of subscription events, just a list of all subscribers.
Also worth noting, is that there are certain situations which can cause a change to a subscription object, these include a change in payment method, cancelling a sub and resubscribing, or subscribing at a new tier. And in the case of subscribing as a different tier, it’s possible for the user to show up in the list multiple times, as both the old tier and the new tier so keep that in mind. Because of this the created_at field is an unreliable way to determine length of sub.
If you want a real-time (or close to it) way to get subscription events, use Pubsub, or Chat, or when it’s released the webhook.