But when using a CBA as an assessment tool for skipping a particular years curriculum, one isn't really testing what a teacher taught per se as that particular curriculum hasn't been taught to the student.

While a CBA should be closely aligned to a curriculum, should it only match one of several curriculum resources used in the delivery of the curriculum? Ex If the PA core says "Apply place value understanding and properties of operations to perform multi digit arithmetic.", why can't a kid just demonstrate in any way on a CBA vs having to answer a question using a specific method they may or may not have learned? Is/Should a CBA testing a specific method (like using a numberline) of adding or testing the ability to add?