There's often a bunch of different versions in nixpkgs. For example, postgres currently has 11 through 15 available (https://github.com/NixOS/nixpkgs/blob/e7f34

There's often a bunch of different versions in nixpkgs. For example, postgres currently has 11 through 15 available (https://github.com/NixOS/nixpkgs/blob/e7f345ca81f4f5513c4e73f3f7b3a3d045f74845/pkgs/servers/sql/postgresql/default.nix#L209 https://github.com/NixOS/nixpkgs/blob/e7f345ca81f4f5513c4e73...). Nodejs has 14, 16, 18, and 19 (https://github.com/NixOS/nixpkgs/blob/e7f345ca81f4f5513c4e73f3f7b3a3d045f74845/pkgs/development/web/nodejs/v14.nix https://github.com/NixOS/nixpkgs/blob/e7f345ca81f4f5513c4e73...).