Shared files on the network are cached by ultrapeers. If a host leaves the network or removes some or all of the files they are sharing it can take a notable amount of time before the cached the files are removed by all involved ultrapeers. This can mean one or more hours. That is one downside of DHT for example (though the advantages of DHT outweigh its downside.) So there's a high chance a percentage of all search results are redundant (the host sharing the file is no longer on the network or sharing the file.)

I am aware some people remove their shares mid-way through sessions. They obviously have their program set to automatically share downloaded files (the default of most programs.) I've witnessed this first-hand many times after browsing them. I was able to download one or a few or maybe only a part of a file then it stops. A re-browse of the host shows them no longer sharing the file. This always annoyed the life out of me. These are people who probably don't really wish to share files but they are ignorant how to properly configure their program. (I've also witnessed this whilst they were presently downloading from me & has happened many times over the years.)

It appears browse-host can also be affected by DHT as it does not always update the host's shares properly between browses.