Although tagging a referrer artifact manifest is discouraged, it is still doable. However, re-tagging is implemented as pushing the exact manifest again to the remote server. According to the distribution-spec, if the remote server does not support referrers API, it will go for the referrers tag schema case. However, it is not necessary since the manifest is already there, we are just adding a new tag not really pushing a new manifest.

In summary, tagging a referrers manifest should never go for the tag schema even if the server does not support referrers API since the referrer manifest is already there on the server.

Originally posted by @shizhMSFT in #1435 (comment)