If a result shows up, it should be available (at least with a proper current client). Some bad older clients used to report files that may have been available weeks earlier. Not good.

However, a source may say a file is available, and then afew minnutes later the source might go offline, or be busy serving up the file.

Also, if you make too many requests from a source that only has a few slots available, your requests may be temporarily banned. For example, if I browse someone with a lot of files and try to repeatedly download more than the usual 3, then that source might automatically ban me as a "banned greedy client."