An NCR set is a form in the sense 3.4 means, and a plain one at that: a duplicate book exists to be written on and torn out, so both halves of the quarter rule fail at once. The absolute rule in that paragraph settles the rest, since a document designed to be completed and handed over is standard-rated whatever its area. Section 8 removes any doubt by listing invoices, delivery notes, order books and forms, receipt books and forms, and record books as standard-rated. Adding a printed terms page inside the cover does not change what the pad is for.
What decides it?
Nothing. Writing on it and tearing it out is the whole purpose.
Where does this come from?
HMRC VAT Notice 701/10, section 8, HMRC's guidance on zero rating books and printed matter. See the notices we work from.
Some real jobs
Duplicate invoice books in NCR20%
Invoices and receipt books are listed as standard-rated.
Triplicate job sheets for engineers20%
Completed and detached, which is what 3.4 separates from leaflets.
A printed instruction booklet supplied alongside the pads0%
A separate supply of a booklet, judged on its own.