Also, FWIW, "low" urgency packages are now only held in unstable for 5 days before migrating, not 10 days. I don't know whether this is temporary or permanent. If permanent, there isn't much of a reason for "low" urgency anymore.
I recently prepared a package and set the urgency to "low" because I made changes in a number of source code files all at once to support a data file structure change. I intended the package to sit in "unstable" for 10 days to give time for any catastrophic error to surface, which is how I discovered this. I just mentioned this as an aside at the end of bug report #868281 but figured I should also add that info to this bug report. Thanks, Paul Hardy