Import directors from Companies House when creating a client. (Company number entered)
Store this information on a client level rather than on the accounts, so that the information could carry though each year.
Add functionality to refresh data from Companies House, new directors, dates of resignation etc.
Directors with relevant dates would be shown in the accounts.
Importing directors and Companies from Companies House is possible with IRIS Elements Tax and Accounts and the Client Management functionality built around that. Once migrated from Taxfiler this will become available to you.