Sometimes a cover makes it back home with only one cancellation

In a previous post I mentioned that some postal workers should be fired.
Here is an example of a cover that made it safely back home with only one postmark done on the first day of issue of one of the Canadian stamps for the IYA.
By some mysterious event this cover did not get any ugly mechanical cancellation even though it went through the same central postal distribution center as the other 2 shown previously.
Go figure!?!