IHTM10802 - Accountability: what is to be included in an account?
The accountable person is required to deliver an account specifying to the best of that person’s ‘knowledge or belief’ all ‘appropriate property’ and the value of that property. The account must be one that is prescribed by the Board, IHTA84/S257.
The meaning of knowledge and belief was discussed by Walton J in CIR v Stype Trustees (Jersey) Ltd  STC 394, CTT Cases No 27 (from page 15).
‘Appropriate property’ is any property to the value of which the tax is or would be attributable. But this rule is modified (IHTM10812) in the case of transfers on death.