Feb 28, 2024

Since milestones exist to mark a known place on the road, but not force you through it (unlike a checkpoint) they are just perf optimizations. They are only useful for headers first, and cannot optimize headers (though that is not in need of it). So once a header reaches that point the blocks under it do not require validation (presumption of previous verification by the node owner). This implies only one is necessary, since block download won't start anyway until headers are "current" (top is recent in time).