The coin changes design several times. When it is given to Gibbs, the design is not a Liberty Seated dollar, but when photos are shown and when Arturo puts it on the car hood it is correct.
When "Arturo" is sitting in the crypt after returning from Vietnam and talks to "Aunt Bertha" he is wearing the same 2 ribbons he had before his deployment. Having served in Vietnam or its contiguous waters or airspace he should also at least be wearing the Vietnam Service Medal ribbon (awarded by the US) and the Vietnam Campaign Medal ribbon (awarded by the Republic of Vietnam).
When Kasie is in her lab discussing the "Million dollar dollar" she is holding it in her bare hands. Apart from her normal mode of handling evidence (gloved!) she would be aware that skin contact could pare hundreds of thousands of dollars off the value of a pristine item. Correction: the coin is in a clear protective container, so Kasie wasn't holding it in her bare hands.
When Palmer and Bishop go in where "Annie Dowling" is buried, they go through the door and her crypt is to the left. When "Arturo" is sitting by her crypt and "Aunt Bertha" comes in "Annie's crypt is straight in from the door.
When Torres brings Arturo's letters that were sent to Annie, to show them to Gibbs and Sloan, they bear postage stamps. Since Arturo was writing from the Vietnam war zone, they instead should have had the word "Free" where a stamp would go.
Ducky refers to Art's papers as "this ephemera". Someone as punctilious about his speech as Ducky is would have said "these ephemera".