Sorry, I thought I'd double post to clarify here.
This is not the alternate method! This is how the spreadsheet is supposed to be used!.
As you wrote in your previous post, there is no way for any spreadsheet to calculate the costs for formulas not publically available (e.g. VIC registration based on post code, NSW CTP based on numerous factors). So prospective owners should be using this to figure it out themselves.
If they don't do it themselves, you are correct, we can only approximate based on the information available (which is what the VW pricing site does btw). But as I said in the previous post. Even in this case, the spreadsheet still makes that task far easier.