I think a while back there was an issue with how the 10.14.6 and 10.15.7 updates were listed from the softwareupdate -l command. This is what the list command shows:
10.14.6:
Software Update Tool Finding available software Software Update found the following new or updated software: * Command Line Tools (macOS Mojave version 10.14) for Xcode-10.3 Command Line Tools (macOS Mojave version 10.14) for Xcode (10.3), 199250K [recommended] * macOS 10.14.6 Update- macOS 10.14.6 Update ( ), 3037755K [recommended] [restart]
10.15.7:
Software Update Tool Finding available software Software Update found the following new or updated software: * Label: macOS Catalina 10.15.7 Update- Title: macOS Catalina 10.15.7 Update, Version: , Size: 5122619K, Recommended: YES, Action: restart,
I tried using "macOS 10.14.6 Update- " and "macOS Catalina 10.15.7 Update- " to download those updates, but then is says:
Downloading: macOS 10.14.6 Update- macOS 10.14.6 Update-: No such update No updates are available. Software Update Tool