A new feature of the site is Variations of a Story - this is when there is another version of a story that is different enough that it should be completed and rated separately, but it’s not actually a different story.
Example:
The Underwater Menace is a story from 1967 which is lost and so only exists as telesnaps, and The Underwater Menace Animated Reconstruction is a reconstruction of the same story with animated graphics.
If you are aiming to watch everything featuring the Second Doctor, and you watch either The Underwater Menace (telesnaps) or The Animated Reconstruction, either will count towards your goal, and you do not need to watch both.
Another example are the various omnibus editions released for Tales of the TARDIS. This also applies to TV Soundtrack versions of stories and Audiobook versions of books.
(Something which is similar, but not the same, would be an “adaptation” - this is where a TV story has been adapted into a novel, or a novel adapted into an audio drama. These are considered different enough to warrant being completely separate stories).