I think a lot of people (and even Disney CMs) are failing to realize that most of the time the day you activate an AP is the same day you first use them, so people don't pay attention to the distinction between the dates in Disney ticketing rules. There are 3 dates which may or may not be the same:
1st is purchase of a voucher (which gets you FP+ access)
2nd is "activation" at a ticket window or guest relations
3rd is first use to enter a park
For an annual pass, the date of activation starts the expiration timer, not the date of first use. The only exception to this is if you are upgrading a previously used ticket to an AP, only then do they go by the first use date.
Think about it this way, if an activated annual pass didn't expire until you started using it to enter a park, you could activate one but never use it to enter a park and would have lifetime access to free parking, merchandise discounts, room discounts, PhotoPass downloads, and all other benefits of an annual pass, but without the annoying expiration date.
No doubt about it, APs start their expiration timer at activation. But you would only notice a difference if you activated your pass on a day sooner than you enter a park (such as activating at Disney Springs on your arrival day, but not entering a park until the next morning, then the pass would start expiring at Disney Springs).