Not entirely, if I recall correctly. The BB Revealed special aired on April 11 2001, but the show didn’t broadcast until April 24. Despite the HMs entering on April 23, I don’t think they were in lockdown for over two weeks? Unless I’m mistaken.
And as
@matts bb said, we used to get snippets of the build and close-up hints of the new design/furniture pre HM lockdown in
both Ten and Nine eras. I even vividly recall photos of the 2005 (or 2004?) house being built from the ground up, after they demolished quite a significant chunk from previous years.