I can't find the thread where it was mentioned: a photo of Irinas sunburst tiara being examined after it was found hidden in the StPetersburg palace by the bolshevics, and the confusion of a photo wearing what looks like the same tiara in the 1920s.
I think I can solve this riddle. I believe the photos weren't taken in the 1920s at all, but BEFORE the revolution, sometime between 1914 and 1916.
One has to remember Irina was a woman on the cutting edge of fashion with the means to indulge it. The slimline styles we often assume as roaring twenties were already established by 1914. See this image for example:
http://www.fulcrumgallery.com/print_37723.aspxYou'll also see that Irinas hair isn't shingled, but merely gathered at the back, which is typical of the prewar period.
The wealthy women of StPetersburg were always right at the edge of style, taking up the tango, etc. I remember one memoir saying that tiaras were out of fashion shortly after 1900...hence the craze for aigrettes - which again, one sometimes thinks of as being purely 1920s. Wrong! There's a Pre Rev photo book which has a pic of female aristocrats in the street in 1916, and they look very modern and chic, and I've seen on of Irina visiting Archangelskoi around that time, and looking very slimline.
I hope this solves the puzzle!