Investigating the assets on page 6 : Pensions (box 56)
You should check the other guidance available on GOV.UK from HMRC as Brexit updates to those pages are being prioritised before manuals.
Any money that was due to the deceased from a pension scheme, either as a lump sum or arrears payable up to the date they died will be included in box 56 of the IHT400. Details of the pensions themselves will be given on form IHT409. Guidance on how to investigate the values and information given for pensions can be found at IHTM17001.
Form IHT409 should include details of any guaranteed pension payments and form IHT410 should give you details of any guaranteed annuities. Both should be referred to the Actuarial Team for advice. We will not normally receive a breakdown of any other type of income owing to the deceased. In general, other than referring the above payments to the Actuarial Team, you do not need to raise any enquiries on the values returned for income in this box unless you have evidence to suggest that the sums returned are understated.