Circa, it means around or approximately.

Thank you, it had confused me for a while because I got no related search results on Google.

Interesting, I never knew that.

There is the matter of no date being set on name event.

For example, we know Star Wars: Episode IV A New Hope was released on May 25, 1977. But what if the date was unknown? Or all you know is the year? Or heck, even the date range? Then your solution would use circa for your estimation, like c. 1977 or c. 1970s in one's comment.

Of course, bear in mind, this is only if the date in question is unknown or unconfirmed. Like there being literally no source to back up the dating information in question.