I cannot read the article due to elsevier being cancer, but I thought it was illegal to deal with ivory at all, no matter how old, because a strict prohibition simplifies policing of ivory (as elephant poachers cannot pretend they merely found centuries old ivory laying around somewhere.)
> Under Federal law, you can sell your African elephant ivory within your state (intrastate commerce) if you can demonstrate that your ivory was lawfully imported prior to the date that the African elephant was listed in CITES Appendix I (January 18, 1990). This documentation could be in the form of a CITES pre-Convention certificate, a datable photo, a dated letter or other document referring to the item, or other evidence.
> The sale of African elephant ivory items across state lines (interstate commerce) is prohibited, except for items that qualify as ESA antiques and certain manufactured or handcrafted items that contain a small (de minimis) amount of ivory and meet specific criteria.
Maybe in some places, but the international treaties allow even commercial trade of certified antiques. And moving a sample for scientific purposes like here is likely allowed anyways if properly certified. The article explicitly references the export permit.
