Hilton aspire annual fee prorated

I upgraded to a Hilton Aspire card 3 days before my anniversary. However, recently, I was only charged $524 for the annual fee. I am wondering, why is it prorated if I upgrade before my anniversary starts. Did they not count me as having the aspire card until like a week after I got it ?

And in anyone else’s experience, would this mean I’m not receiving my anniversary free night ? Or my free night for upgrading? Keep in mind this upgrade was in late February during my first year if that matters so I guess I didn’t complete a full year of having the Hilton honors no annual fee card before upgrading it (I don’t think this is relevant just adding it in case).