Something weird happened with FZROX on the 12th. Then the S&P followed suit on the 14th? How can this be, what happened. (see image)
The index funds are different portfolios, both attempting to mimic the S&P. They are balanced slightly differently and have different %'s of different investments so they will not be exactly the same. You could google both and find out what their holdings are/were if you want to find out exactly what was different at the time.
...but the are very close all the time, and then for that one period of time, fzrox dropped over a day before the other index. Did the 2000 they hold, somehow drop days before the 500 the other holds? ...and then when the other dropped, fzrox didn't? That doesn't make sense to me no matter what their exact holdings are.