Pretty well no because most of those repos are now closed.
not fully correct.
most upstream repo have been put in archives needing you to know how to configure them to use them.
some have just disappeared.
and finally SME and base centos are normally configured to let you minimal access to fully upgrade to last sme state before you migrate. For that to work you might need to update individually smeserver-yum package.
Remember this is not to let you keep it working long after the EOL, this is to help you migrate, knowing that you might need last backup tools available.