IHT - Is use of IHT415 interest in another estate required?

My father died 2020 leaving everything to my mother (They were married). She obtained probate. Most of the administration completed, but one investment OEIC is still "Estate of Mr X". My mother died recently and we are completing IHT forms. Is it necessary to complete the "IHT415 Interest in another estate" form, or is it acceptable just to include this OEIC holding in "IHT411 listed stocks and shares" form?

Hi,

Please contact the Inheritance Tax team for advice.

Inheritance Tax: general enquiries

Thank you.