At one point Benjen Stark states that
The Wall is not just ice and stone. Ancient spells were carved into its foundations. Strong magic to protect men from what lies beyond. And while it stands, the dead cannot pass.
However, at the beginning of the series...
...a deadman/wight attacks Jon Snow in Castle Black, which is situated on the other side of the wall.
Also in the latest episode...
...a wight was taken south of the wall on the back of a dragon.
These two instances seem to be at odds with Benjen's claim that the dead cannot pass the wall.
Is there any explanation for this?
By "the dead" I only mean the deadmen/wights/animated corpses - not the Night King or the White Walkers.
By "cross the wall" I mean anyway of going from one side of the wall to the other, including flying over, tunnelling under or passing through.