I still don't understand why the posting date would be blank, even though I "reset" (cleared) the date and then posted it. It shouldn't matter whether the original announcement was imported or not; it was posted at a particular date and time. That date and time should show. Also, it has never mattered in the past 10 years, but suddenly this past year, dates aren't showing. I've imported and recycled announcements at least 40 times over the past 10 years, and never had this issue.
This may be related to the photo issue linked, in that both are problems with imported announcements, but at least there was a rationale given for the photo decision (I don't agree with it, but I do respect that some thought was involved). This one just makes no sense. The post date is the post date, and it is important that the date actually show up on the post. We are accountable for providing timely information, and sometimes we actually are called to account for those. Blank spaces where dates should be don't help us or our students!
What this is all amounting to is that course imports don't really include announcements any more, in a meaningful way. If the announcements are going to be broken and un-fixable (even by resetting the posting date information), the import hasn't really worked.