Beth, I have also downloaded that photo of Queen Mary from the ILN website (in 2012) without realising the significance of the tiara & the dates - only that it was the first one of Queen Mary with her Garter sash.
But below the photo of Queen Mary it states that her son, the Prince of Wales will be declared a Knight of the Order at Windsor Castle on June 10.
1911 was a busy year for their Majesties: 10/06/1911 Garter Ceremony at Windsor 22/06/1911 their Coronation at Westminster Abbey 13/07/1911 Investiture of Prince of Wales at Caernarvon Castle 12/12/1911 Durbar in Delhi
It seems as if it really was published in May 1911 before all these ceremonies took place & that Queen Mary got hold of the tiara for a preview & photo! Royal collection's dates may be linked to Roberts recording of the Garrard's invoice but this ILN photo really seems like evidence to me that the tiara was able to "carry" these Cullinan diamonds in 1911.
--Previous Message-- : : I think the title and date printed on the : ILN is sufficient evidence of the date of : publication. : Of course it is not evidence of the vintage : of the photo. : : :