They can control their pheromones and can pretend as a beta. They appear in trait test as a beta. This gave a lot of problems and misunderstandings in Koi’s traits before because Ashley was showering him with pheromones to turn him to an omega from Beta but Koi never mutated and always appeared as a Beta in trait test. This is also one of the reasons why Ashley’s father had them separated. Because despite Koi being a Beta Ashley wanted to marry him after becoming an adult (Yes their relationship started young like 15 or 16 years old base on the novel)
Anyways it turns out Koi is a Dominant Omega. Even after they’ve done the trait test when he was pregnant it still appears as Beta. This is the reason why a dominant omega can hide if they wanted to. They are after all a very rare trait an ultimate dream of every dominant alphas.
Remember Angel? Kieth’s birth mothet? Angel was abducted when news about his traits was revealed and he was forced to conceived five children one of each for 5 families. That’s the reason why Angel told Koi to never acknowledge him because if others knew he might end up the same faith as him.
After Ashley found out he is a dominant Omega it was kept a secret until their wedding where finally Ashley marked KoI as his Omega on their first of their wedding.
When Koi and Dane met Koi had hide the fact that Dane is a dominant Omega for thr same reason. When Koi and Ashley’s youngest child manifested as a dominant omega Ashley took precautions because of it. No one knew of it except for the family and Doctor Steward. He even decided to send Bliss to England to avoid for sibblings to lose their minds to pheromones of their youngest sibling. Ashley said, as soon as all his elder siblings find their mates or person to love then it will be safe for Bliss to comeback. Just then they will just visit him in the England.

Wasn't he supposed to be a dominant omega, not a recessive? Or am I forgetting something