from GitHub's transparency report:
https://github.blog/2022-01-27-2021-transparency-report/#Nat...
"We’re very limited in what we can legally disclose about national security letters and Foreign Intelligence Surveillance Act (FISA) orders. The US Department of Justice (DOJ) has issued guidelines that only allow us to report information about these types of requests in ranges of 250, starting with zero. As shown below, we received 0–249 notices in 2021, affecting 0–249 accounts."