On a constituent record, the Event registrant constituency's date from value reflects the day that the event registration was added in CRM, not the date of the event.
We are currently evaluating this issue for a fix in a future service pack.
Steps to Duplicate
1) Create a new constituent. 2) Using the new constituent, add a registration for an event that has already taken place. 3) Add a payment for the event registration, using the date of the event as the revenue date. 4) Go to the constituent record > Personal Info tab > Constituencies sub-tab > Notice that the Donor constituency's Date from correctly reflects the revenue date but the Event registrant constituency's Date from is today's date.