I wonder that as well, as I have not seen formal family portraits for every year, only 1896, 1898, 1899,1901, 1904, 1906, 1913, I have not seen any other proper formal photos from other years.
Being a Royal Family I would have thought that one would exist of them for every year.
The children had a series from 1910 and 1914 and a few when they were little but apart from the photos in court costume that is it that I have seen.