In the past, it was almost-always possible to get offline installers for Apple macOS updates from https://support.apple.com/downloads/ (you get a PKG file in a DMG file).
However the same doesn't seem to be true for Catalina. So far none of the updates have been made available.
- Supplemental Update 19A602
- Revised Supplemental Update 19A603
At-least not in the usual place, they can only be installed using the built-in software updater.
Are these being made available for download somewhere, or is there any more information available on this issue?
Sometime late yesterday or early today the 10.15.1 update was made available for download (along with corresponding 10.14 Mojave Security Update 2019-001 and 10.13 High Sierra Security Update 2019-006 updates; 10.12 Sierra is likely retired now).
The 10.15 Supplemental Updates were never made available in this way for some reason, but the 10.15.1 update supersedes those updates anyhow. It remains to be seen if other 10.15 updates like the Security or Supplemental updates will continue to be available as they were in the past.