I want to point out that I do not regularly look at my own profile, so my likely, I was promoted on June 30July 1 (when I posted after the new activity period), but did not notice until yesterday.
Ah, that might explain the problem here. I was always under the impression that the transition from Hero-->Legendary happened on the day of the activity period change. I'm pretty sure that was the case when I made it to Legendary, because I was anticipating it for weeks on end (I finally made it when I had an activity of something like 1064).
If anyone got ranked up to Legendary (or any other rank for that matter) in any other point during an activity period than the first day, I'd be interested to hear from. That--to my knowledge--isn't how it works.