When magic works...
...it works fast and unseen. The changes in reality are hard to reckon if you miss the point when they happen. Afterwards its nearly untraceable, it is just normal behaviour of things, as usual in history. Sometimes you can find the spot where it happened when you have a very sharp eye: When the door was closed five minutes ago and the changes that happened afterwards just could never have happened if the door was not open there must have been a spot in time when someone opened it ...but perhaps you have got the only key.