Based on the date, this unmasking list for Flynn was likely prepared in connection with POTUS and Coates reforming unmasking policy in general. Meaning there are more such lists. The list was not prepared specifically for the Flynn criminal case. https://www.dni.gov/index.php/newsroom/press-releases/press-releases-2018/item/1832-dni-coats-establishes-new-intelligence-community-policy-on-requests-for-identities-of-u-s-persons-in-disseminated-intelligence-reports

@walkafyre points out that “dated” may refer to the date of the manual referenced above that date. I can’t (yet) find a version of NSA/CSSM dated or updated in 2018, but that doesn’t mean there isn’t one. https://www.nsa.gov/news-features/declassified-documents/nsa-css-policies/