apt-offline directory and upgrading from 16 to 18

I followed this: https://www.debugpoint.com/2021/03/how-to-update-or-upgrade-ubuntu-offline-without-internet/

I'm trying to test an offline upgrade from Ubuntu 16 to 18.

The "offline-data-dir" created just now is only 40MB. That can't be right?

I copied that data to a Ubuntu 16 and pretty much nothing happened when I ran apt-offline install offline-data-dir/.

If I understand... I can run apt-offline from the Ubuntu 18 machine, copy the offline directory to my Ubuntu 16, then just run the above install command?

I guess I would have expected the offline directory to be a few GB at least.