Well, the real problem is Kirk changed our timeline when he came back to 1986 to get them friggin' whales.
No, he didn't.
There's no evidence that he did, at any rate. (Up until Kirk and crew left 2286 to journey into the past, we had not heard what happened to George and Gracie.) All the data we do have, suggests that there were no changes to history.
They returned to the same timeline they left, after all.