Now that I am back online I have been able to do some searching. Initially I was taken with the similarities between the shape of the elements in the Countess of Wessex's wedding tiara and that in the small tiara worn by Queen Mary in 1901.
Then I saw that, in 2013, Nellie had posted 2 photos from the same series as the one I posted. (I found mine in the records of the Patents Office, Victoria. The originals are now held by the State Library of Victoria.) Modern reproduction techniques for the book Nellie used have resulted in much clearer images.
The photos Nellie posted suggest to me that the elements in Queen Mary's small tiara are different from the ones in the Countess' tiara.