The estimates are a baseline, and then through supplementary estimates (A), (B), and (C) you get additions to the baseline based on the budget for that particular year. So it is part of the picture. I think it would be unwise to say the main estimates are the whole picture, because quite frankly, they are subservient to the budget, and of course there's a lot of debate in the House of Commons on the budget.
On March 10th, 2015. See this statement in context.