Hi,
Something just brought to mind apt-offline. The introductory paragraph
in the man page states:
apt-offline brings offline package management functionality to Debian
based system. It can be used to download packages and its dependencies
to be installed later on (or required to update) a disconnected machine.
Packages can be downloaded from a different connected machine.
Don't know how suitable it would be FOR ME. However studying its use may
prompt questions &/or answers I haven't thought about.
From looking at the source[1], apt-offline seems to be looking in the
local cache first before fetching files from the Web.
[1] https://github.com/rickysarraf/apt-offline/blob/master/apt_offline_core/AptOfflineCoreLib.py#L1231
Alex