I've been doing the same for about 15 years, except I actually send the emails to myself and have a special tag for them. Unfortunately, Gmail search has failed

I've been doing the same for about 15 years, except I actually send the emails to myself and have a special tag for them. Unfortunately, Gmail search has failed to find things for me in recent years that I know are there and know are tagged with a particular key phrase, usually for things that are from the 2009-2013 time period. I've lost faith that they are actually keeping everything, or perhaps that they are keeping everything but their search algorithm may sometimes return "no results" in order to be fast instead of actually falling back to some kind of deep search.