Ok so this is interesting. I just logged onto my Horizons only Alt, who delivered no more than 3 tonnes to any of the bridge CG's for the sole purpose of expanding the reward pool.
She doesn't have the Emissive white or any of the metallic explorer decals, as expected, but she does have the Red and Blue explorer decals, and in her inbox she has this:
Wonder what will actually show up.
My main account that actually did have top 10% in a couple of phases also got the same message, but still doesn't have the red and blue emissive explorer decals.