When Dinozzo and David are interviewing PO2 Borrows on the Majestic, she has an Enlisted Surface Warfare device on her Coveralls. In the next scene, when she is at NCIS, there is no Enlisted Surface Warfare insignia on her NSUs.
Abby matches the bullet fragment to Gibb's rifle. Unless his rifle has been in storage all that time, not possible. In twenty years, it would have been re-issued to a stream of marine snipers, who would train with it or use it on deployment. The wear would change the rifling marks. In twenty years, it would probably have had a worn barrel replaced at least once, completely changing the rifling marks.
Petty Officer Burrows appears several times in a dress uniform. The blouse is khaki colored. Prior to 2009, the only enlisted people to wear khakis were Chief Petty Officers E-7 to E-9. Petty Officer Burrows would have been wearing a dress white blouse if summertime or black blouse if winter. However, the Navy enacted a uniform change that took effect in 2009; sailors E-6 and below now wear a khaki top with navy blue (almost black) pants. Petty Officer Burrows' uniform is therefore correct. Further, this is not a dress uniform, it is an everyday working uniform entirely appropriate for the setting.