Thank you, Malcolm.
I managed, eventually (Wow, it's slow !) to find the Model Crowns listed in the Fitzwilliam Museum and they have seven varieties listed ... CM.2968-2003 to CM.2974-2003 starting on page 550. All the varieties are listed with the 'issuer' as H.Hyams, including the '18 48' (instead of H.Hyams) variety and the 'blank' (instead of H.Hyams) variety, which are both attributed to H.Hyams as being 'inferred'. However, unfortunately, they do not have the G.Dee variety listed.
I wonder what is listed in A.K.Barter's book, 'Model Crowns volume 2' ? .... I would love to see a copy of his book on the subject.