The updates are NOT standalone.

You need to download the switchroot L4T version specified in the tar.gz name, and then patch it with the updates here.

Example: "update-1-for-switchroot-l4t-ubuntu-2019-04-28.tar.gz" is an update for "switchroot-l4t-ubuntu-2019-04-28.img.gz"

You only need to install base image and the latest update unless specified otherwise.