Hi The number in the block id comes from the 'delta' used to define the block by the module in hook_block, not the order in which they are rendered.
Lee >The reason behind this is that I want a certain block that is generated by a certain module to be numbered based on its >appearance inside a page. I'm surprised however, that the block rendered in the body gets a #1 and the one in the >header gets #2 although the one in the header was printed before the one in the body and although the header region >was declared before the body region in the theme .info file.
