Validate combines several separate checks, rather than relying on one.
Clear rules at upload. The writing sample must be the student's own earlier writing, not AI-generated, at least 500 words, and separate from the work it's compared with.
The writing sample is only part of the picture. The student still answers questions about their own submission (Cognitive Command), and Validate still assesses Human Factors in the submission. A matching writing sample can't make up for weak results on the other dimensions.
You make the final call. You see Authorship Continuity alongside Cognitive Command, Human Factors and the student's answers.