From our school IB coordinator. Definitely the highest grade. Not the latest.
Your grades can go down after a remark BUT if your request was with written consent, the original grade will be reinstated.
You can get this directly from the IBO too.
"Can a request be made for a re-mark of a DP or CP candidate’s work, and can a grade go down if re-mark is requested?
If a candidate would like the IB to re-mark their work, they should approach their school’s DP/CP coordinator to discuss available options since he/she would need to place the request (called enquiry upon results) on the candidate’s behalf. Please note that this service is not free of charge and it is the coordinator’s duty to inform the candidate (and/or legal guardians) of the fee involved. The IB will not accept requests for re-mark from candidates or their parents/legal guardians directly. In addition, the IB will not communicate the outcome of an EUR request to anyone other than the school’s DP/CP coordinator. As there is a possibility that a grade is lowered, written consent from the candidate (or legal guardian) is required. Should a school not obtain a candidate’s/legal guardian’s consent prior to placing this request and the grade is lowered, the original grade will not be reinstated.