Neela graduates in this episode despite stating she is in her third year in the beginning of the season. As has been depicted numerous times in the show, U.S. medical school takes four years (for instance, Abby is in her fourth year in this season).
The plot line around Abby passing her boards is not quite accurate. A practicing physician is required to be licensed, which requires a set of exams during med school and residency; but a physician must not necessarily pass a board exam, which is a higher qualification in a specialty (though it is quite common for physicians to do so). It is certainly not necessary to pass boards to graduate medical school, since these exams would be taken towards the end of or after a residency program and specialty fellowships. Abby would take a licensure exam at the end of medical school which scores would help her attain a residency, but even this exam is not necessary simply to graduate.
Samantha tells Neela and Abby about the times when Steve would pick her up at school in his "Mustang GTO that he was always fixing." There was a Mustang GT, and there was a Pontiac GTO, but there never was a "Mustang GTO."
Neela and Abby should only be 3rd year students since the beginning of season that's what Neela was and Abby dropped out in 3rd year. Rachel should only be 16 yet she is acting as though she is going to start college that year.