It depends on whether you are using HTML 5 in which case you can surround the entire post in an article container. That might go some way to making it less sematically problematic.

Even in that case though a header is a hierachical indicator, so just as an h2 subdivides the article in a way that you can’t break back out of (all content after that point is a sub-section, or sub-sub-section etc) the H1 signals that everything that follows is content under that title.

In most cases the date and attribution, while not part of the article itself, is part of the content that falls under that header so you would expect it to be positioned after the header.

Placing the date and attribution before the header effectively renders it applicable to the content that comes before the header, or to the page in general; although again, you would expect the H1 tag to apply to the page unless using further semantic divisions as is possible in HTML 5.