I can confirm that it must be your original BO, the one with a yellow name. I had a USN and KM BO past 30, and while I received access to ECLs for each of them, it was not until my yellow-named SN BO reached level 30 that I received the elite engineer and two premium sailor boosts (in addition to the SN ECL).
It's a shame, because my KM BO had just hit 45 today and at midnight the event will be over.
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