Retention period for accounts requires preservation of books until the post-return deadline, extended by appeals or investigations. Registered persons must retain books of account and other records until seventy-two months from the annual return due date. If the person is party to appeal, revision, other proceedings, or under investigation for an offence under Chapter XIX, records relating to the subject matter must be kept for one year after final disposal of those matters, or for the seventy-two month statutory period, whichever is later.