Hi Rungroj
I looked through EI 1550 2nd edition and on Pg 60, it did clarify that the latest edition of 1596 was primarily intended as a guide for acquisition of new vessels. It leaves end users the discretion if they feel their existing pre-1596 vessels are fit for purpose and if so, no change is necessary.
Please advise BAFS and if they have any questions, let me know. I have attached the page for your reference.