those "surprise" disappearances by directors under the age of 70

介词by 可以引出动作的施事者，即行为主体，直接放在名词、动名词或具有动作的名词之后，作定语，说明是由by 后面的名词完成的。例如：

books by Lun Xun = books written by Lun Xun （鲁迅写的书）

bombing by planes = bombing performed by planes = （由飞机实施的轰炸）

At Smith she turned down a request by students to have race-specific dorms.

在史密斯大学，她拒绝了学生提出的按种族分住公寓的要求。

They are trying to avert a strike by the actors.

他们正设法要免除一场演员举行的罢工。

The city was thrown into turmoil because of a protest by taxi drivers.

由于出租车司机的抗议使得该城市陷入了混乱。