My guesses for the Japanese New Years Reception:
Masako: Meiji Tiara, Chrysantemum Diamond Tiara or Honeysuckle Tiara
Aiko: Sayako's Tiara
Kiko: Pearl Sunburst Tiara, Akishino Diamond Tiara or Diamond Scroll
Kako: her birthday Tiara
Yuriko: her diamond kokoshnik Tiara
Nobuko: her Pearl and Diamond Tiara
Hisako: her Diamond Bandeau, Pearl and Diamond or her Pearl Drop Tiara
Tsuguko: her birthday Tiara
Akiko: her birthday Tiara
Hanako: her Wave and Sunburst Tiara
Yohko: her birthday Tiara
My guesses for the Luxembourg New Years Reception:
Maria Teresa: Belgian Scroll, Chaumet Emerald or (surprisely!!) Empire Tiara
Stéphanie: Adélaïde's Sapphire Tiara, Citrine and Pearl Tiara or Chaumet Pearl and Diamond Tiara
Claire (if attending): Diamond Vine Leaves or Adelaïde's Sapphire Tiara
Alexandra: Amethyst Tiara, Chaumet Pearl and Diamond Tiara, Diamond Floral Tiara or Diamond Vine Leaves Tiara