The existence of the FISA Court has never been a secret. It was created by FISA in 1978 and is right there in the text of the statute. Even the members of the FISA Court are publicly disclosed (they're all existing Federal judges who are appointed to temporary terms).
What is secret about the FISA Court is its decisions, not its existence (and that should change slightly as a result of the USA Freedom Act's requirement to release "significant" opinions).
As a European that still effectively screams "secret court" to me, just with some word games around it. Part of the problem is the US also broadly applies "Top Secret" to too much information, even the mundane, so then it "has to go to the secret court because it's "Top Secret".
Oh, I'm happy with the description of the FISA Court as a "secret court"; I just wanted to answer the misconception that this means people didn't know that the court existed.
Interestingly, regular courts can and do hear cases involving classified information.
https://en.wikipedia.org/wiki/Classified_Information_Procedu...
It's not that cases involving classified information somehow get transferred to the FISA Court; instead, the FISA Court only hears cases involving surveillance requests arising under FISA.
This opinion is just nuts. Trust a court that you were told for years didn't even exist? A secret court? How about no.
Secret courts lead to abuses: https://www.opendemocracy.net/ourkingdom/jo-shaw/secret-cour...