Incorrect Tracking Information

I sent an email to one person with a CC to two other people. I had the tracking option set so that I could see when they read the email. The tracking information shows That I sent the message on 05/07/02 at 6:59 am and shows a status of 1 person reading the message. But then in the recipient information it shows one of the users reading it 05/06/02 at 4:31 pm and one at 05/06/02 at 3:37pm. How can it show that they read it with a date and time prior to when I ever sent it? Their clocks on their computers are correct.