Why a movie can have several watch buttons, and how sources stay fresh.
A "source" is one upload of the film on YouTube. Films often exist on more than one channel — an official studio channel and a regional distributor, for example — so a movie page can offer more than one Watch button.
Our crawler re-checks sources regularly; ones that disappear from YouTube are deactivated automatically.
New uploads on trusted channels are picked up daily (and within the hour for channels we watch closely).
Viewer reports also flag dead links between crawls — see "Report a broken link".