Could be a case of many things.
A while ago I found a death notice in a Police Gazette for a man who died while away working. As he died in the house of the people he was working for it was up to them to fill in the details. They knew he was married with children and that was all. So the police put notices in the newspapers and gazettes (I guess for his wife to read and contact, but as she couldn't read it was pointless)
The poor mans death was never registered, but is listed in gazettes and newspapers.
I guess sometimes the paperwork never made it to where it had to go or got ruined along the way.
Bad enough nowdays let alone back then.
Remember to use * as a wild while searching just incase names were misspelled or mistranscribed.