Possible Clues:

• Range of notes, not English, found with old book
• Loves having rewritten Act 5 in book
• Ring tax company about book of a certain size
• Book shows round about zero tax return
• Zero-tax company turned over in paper?
• 6 x 9 in. book size
• Volume of tax held over by company starting with nothing
• Common book size
• Paper or book size
• Volume specification