Is a nexus letter for migraines necessary if you are still within your 1 year presumptive time frame

I got diagnosed while I was in and have an in service event all the VA said was I need a nexus/link to service

I’ve been to the VA and got migraines in my notes+showed my log to the pcm and she documented, prescribed me with meds and will follow up later. Putting in for a supplemental, nexus letter still necessary?