No you don't need to keep the same search window open.

Beware of dud files. If you find you're getting high search results for popular copyright files, eg: 100 for one, 99 for the next, etc. then those will most likely be spammed fake results. Instead, look for those with 10 or 20 search results further down the results.

Doing repeat searches or varying your search for the same topic, can help find more sources.