You mean… once a year? Because yeah, over 8% of batteries will age out in the month Apple releases a new phone, even with a random distribution.
The window in the normal person’s mind for “they’re doing this on purpose” is probably the month of the event announcement, plus the month the event happens in, and then the month afterwards is when the phones ship and friends start getting them. That’s a solid 25% of the year that would look suspicious to a conspiracy theorist.