Could you please let me know where did you read this information ? Could you provide us with the link ?This was true till they changed the rules. This isn't true anymore.
Now, students may start the program online in September, if they have submitted a study permit application before Sept 15th, and have submitted all docs required for the in-principle approval (except biometrics & medical which can wait).
This time will count for PGWP, but travel is only possible with full approval.
But it's up to the institution - better confirm with them once.