The term linkable means reasonably capable of being linked.
Note to § 202.233:
Data is considered linkable when the identifiers involved in a single covered data transaction, or in multiple covered data transactions or a course of dealing between the same or related parties, are reasonably capable of being associated with the same person(s). Identifiers are not linked or linkable when additional identifiers or data not involved in the relevant covered data transaction(s) would be necessary to associate the identifiers with the same specific person(s).