Deal with multiple docs within a day

[lunakv]

There were two versions of the IPG that were released effective 2017-09-29. The reason for this appears to be some quick errata in section 2.1.

The API retrieves the files by date, meaning it assumes only a single document was released at any given day. We somehow need to account for those two versions existing on the exact same date.

We could just ignore it (as we currently do). That one incident seems to be an outlier, so we can simply pretend it didn't happen and display only the later version of the changes in the archives. This is what we do now. Alternatively, we would somehow have to rework the API to not assume the release date / effective date is a primary key for policy docs. That's more future proof, but also more work.