Thank you.
I think the difference between the two estimates could be explained by the different sources of data that we used to calculate that additional GST created. For example, our costing is based on Statistics Canada's population income projection using a 2017 survey, with some economic adjustment to consider the economic reality in Canada right now. However, I assume that the finance department estimates are based on the most recent T1 database. That's the main source of this difference.
In addition to that, I think that since we are using Statistics Canada data and assuming implicitly that everyone eligible would claim the GST credit, the reality could be slightly different, because some people cannot or don't, or there is no tax field and there is no information on that small percentage of the population. That could also explain the difference on cost estimates between PBO estimates and the finance department's estimates.