I haven't had the opportunity to see the HRSDC study, but the Parliamentary Budget Office was given that study. My understanding is that HRSDC did one costing based on no impacts on behaviour of individuals. The Parliamentary Budget Office thought that HRSDC estimate was an accurate depiction of the costs, so there was no dispute between HRSDC and the Parliamentary Budget Office about a plain vanilla version of costing the proposal.
HRSDC then added onto the cost some assumed impact, saying there would be more unemployed workers if the entrance requirement were lowered. That's how you got the much bigger number.
I hope I'm not misleading people. I think HRSDC came up with two numbers: there was the $1.1 billion, and then there was a higher cost based on an assumed second-round impact.