IHTM10751 | Corrective account (C4S): when is a corrective inventory required (Scotland)?
From HM Revenue & Customs · Inheritance Tax Manual
A form C4(S) is required when the taxpayer or agent needs to obtain an Eik to Confirmation (IHTM05092) after the discovery of assets that were not included for Confirmation. If the taxpayer or agent only needs to tell us about amendments they should fill in a form C4.