The relevant factor is when you began the service for Mate 1600, not when you obtained your current endorsements. You can take the old exams if you have at least one day of service that meets the requirements for Mate 1600 that was obtained before March 24, 2014. You also would have the option of taking the new exams if you prefer.
On Mate 1600, I do not think there were significant changes to the exams that were being given just before March 24, 2014. For other endorsements there were some major changes, but I don't think there were many for Mate 16900.