IHTM31416 | Assessing: calculations: death estate: revision to the original tax charge
From HM Revenue & Customs · Inheritance Tax Manual
If a previous calculation has been issued for the assessment group, you should include in the new calculation the figures for:
the previous value of the property in this assessment group
the tax previously charged on it
the revised value of the property in this assessment group
the revised tax charged on it
This will help the taxpayer or agent to understand how the figures are arrived at.