For buyers contracting authority
Pick 72330000 when the deliverable is consistency itself: data or content standardized to a common model and classified against a shared scheme. A contracting authority uses it for taxonomy and metadata work, for aligning records to a reference standard, or for the standardization activity that has to happen before data can be exchanged across bodies.
The boundary that trips authorities is Data-processing services (72310000). Processing transforms or runs data to produce an output; standardization sets the rules and shapes the data to fit them. If the contract's main job is applying a standard or building a classification, tag it here, not under processing.
The other neighbour is Database services (72320000), which is about designing, populating and running a database as a system. Reserve 72330000 for the format-and-classification layer that sits on top of the data, whatever store it lives in. Where a single contract folds standardization into a larger data programme, set the primary CPV code by the dominant deliverable rather than the whole bundle.