Dr. Gelfand says that Gibbs is suffering from "disassociation". The correct psychiatric term is "dissociation".
It is revealed that Gibbs joined NIS (changed the same year to NCIS) in 1992 following the death of his wife and daughter. However, in the JAG episode "Ice Queen" in 2003 he tells Lt.Cmdr. Rabb that he has been an agent for 19 years, which would mean he would have joined NIS in 1984.
While revealing Gibbs's first marriage and daughter to Ducky, Jenny Shepard says Kelly (Gibbs's daughter) was born in '84, and died as an 8-year-old while Gibbs was fighting in Desert Storm. Fighting or 'Major Combat Operations' of Operation Desert Storm (or Desert Shield) ceased in early 1991. This makes it impossible for Kelly to have been 8 years old at the time of her death.
Kelly was born in '84 and killed in '91, which would make her 7 years old, yet Shepard said she was 8 when she was killed.