Do you know how complete that online database of digital newspapers really is? If a site indicates they have coverage of the Lazytown Leader from 1880 until 1900, do they have all the issues of that daily newspaper or only a smattering? It may be that there are months where no papers are online or only a few issues are digitized.
And this may be the case even if a microfilm copy of the entire set of newspapers exists.
The reason you can't find that obituary for 12 November 1890 may be because there are no online images from November of 1890.