Possible Clues:

• 6x9-inch book size
• Raised zero tax from firm - that's one for the books
• Small book size
• At the end of September, Virginia returns with circle for a sizeable book perhaps
• Certain book page size
• Having eight leaves to the sheet
• Old firm keeping tax returns in book
• Found at the end of the month, a very old sort of book
• Size of book of the month, a volume getting round
• Maybe 50 in the fold after 19 across, in short