Golden Jubilee Sierra Leone $1 crown cover with Guyana stamps

This large sized CrownCover was issued by Mercury in 2002 to celebrate Queen Elizabeth II 50th anniversary as our Queen. It has two $1.50 stamps from Guyana and the crown or Dollar from Sierra Leone that is so special. The reverse shows H.M. Queen Elizabeth II, Prince Philip and two locals enjoying the palm fringed scene. The obverse of the coin has the arms of Sierra Leone. We have never seen this crown before. We think it's because it was struck only for these covers.