From a strict interpretation, in the W3C at least, a specification must be at least a publicly published Working Draft (WD) by an active Working Group (WG) to be on an official "standards track", and thus that should be our condition for explicitly labeling a technology in a W3C document as "standards track".
At a minimum a specification must be accepted into a WG’s charter, and not just as a NOTE, in order to qualify to be standards track. However it’s not actually on that track (and citable as such) per se until the WG has agreed to publish it publicly as a WD.
By at least a WD, I’m explicitly saying yes it can also obviously be a Candidate Recommendation (CR), Proposed Recommendation (PR), or Recommedation (REC, or edited, or amended). If it’s an Obsolete Recommendation we should use the "Obsolete" label.
If it’s only in an Editor’s Draft or a WD (before a CR), that would be reasonable to label as "Experimental", as anything that’s not yet in a CR can "Expect behavior to change in the future."
If a document is for example only developed in a Community Group (CG) such as WICG, it is not standards track (CGs cannot make standards), and thus we should explicitly label any technologies there as "Non-standard", until such document makes its way into a WG and the WG publishes it as a WD, therefore publicly signaling that the WG has agreed to advance it onto the standards track.
For IETF and other orgs, I’ll let others chime in about what state a document must be in to transition between "non-standard" and "experimental" and "standards track", or "obsolete".