The server moniker using the year is the one with Desktop Experience (full GUI). The one using the branch name is the SAC Core release. If a branch has an LTSB/LTSC release, both are offered in one ISO (usually Standard Core + Datacenter Core + Standard Full + Datacenter Full). For other branches, the Full releases are missing. So far, we have Full Server 2016 (1607) and Server 2019 (1809). Next will be Server 2022 (probably 22H2-based).