Even basalt mineralization injection from ClimeWorks Iceland faces a transformation front challenge (as the area near the injector transforms it gets in the way of subsequent transport and transformation). The storage is modelled and not measured. Drill a hole to measure concentration, a new hole.

All options are poor and expensive and slow. And there is no enforcement or motivation to get it right (credit w/o evidence is the standard play in carbon accounting). So, I fall back to the position: if you haven't put it under the continental shelf you haven't done jack. Mostly a good rule.