Shinto religious practice keeps all three objects permanently unshown. Atsuta Shrine, Ise Grand Shrine and the Imperial Household Agency have never permitted an outside examination, so nobody outside the shrines and the Agency has verified the objects present or their condition in the modern era.
What would resolve this A supervised non-invasive examination, such as imaging conducted by the custodial shrines or the Imperial Household Agency themselves, since no outside access has ever been permitted.
OpenShinto studies, archaeometryNippon.com, The Imperial Regalia: Japan's Three Sacred Treasures (Nippon.com)