In addition to tripleo-quickstart, the current-tripleo-rdo tag in some releases or versions of CentOS, if you look in the ci-config repository, included smoke tests of tempest using the packstack environment and puppet integration tests. This gave the tag a greater level of stability. I found confirmation of this in the TripleO documentation (1) at docs.openstack.org and in the Delorean documentation (2). Although the Delorean documentation talks about the current-passed-ci tag, I understood from exploring the trunk.rdoproject.com repository that it is the same as current-tripleo-rdo, but I may be wrong. For this reason, I was concerned about the long absence of new containers with this tag in quay.io. It's very unfortunate that you were forced to make this decision.
You are correct. WRT validation using packstack and puppet, we still run it in a different pipeline in parallel and use it to promote puppet-passed-ci link in RDO Trunk repos, you can see the jobs status for the more recent releases in [1]. I understand that these two validation sets run in parallel and they don't converge in a single tag but note that any issue we catch in puppet promotions will be fixed and patches will end up in tripleo containers.