The opposition (either party) is supposed to put together a fully costed plan for the next three years, some time before the election. In media land that's either "now" (wherever that is in the cycle), when the election is called, or soon after. This plan is then subject to microscopic examination by the media, Treasury and the other side.
For the opposition, that's it. No second chances, no amendments, no false assumptions and God forbid - no errors.
For the government of the day it's business as usual. You can sit there in Jan 2013 and say you can't predict the surplus/deficit 6 months way until you get some new numbers confirmed - and you can say that with a straight face. You can announce something like the Disability Support plan unfunded, so long as you are in office. You clan blow out an NBN by whatever number comes to mind, so long as you are in office. You can handle a few billion extra on a failed immigration policy, that's ok as long as you are in office.
The most treasured (no pun intended) prize is to uncover the holy grail - a Black Hole. That is so valuable that it can be used in subsequent election campaigns as proof of the other side's incompetence.
