Every Celestial Dragon we have been introduced to possess the Saint title in their name yet a certain someone does not have it in any. I believe Shamrock is not pure blooded Celestial Dragon.
Shanks mother was a commoner who got pregnant and gave birth to Shanks and Shamrock. This is why their hair color doesn’t match Garling.
Garling must have loved the woman if he acknowledged his sons and did not throw out the mother with the twins from Mary Geoise.
He had given Shanks a chance to return.
Gunko is a halfblood Celestial Dragon who is not recognized by her Celestial Dragon parents and was also a victim of Saturn's experiments like Bonney. She was recruited as a Holy Knight because they were short on recruits. They were trying to recruit Loki
Those of Impure Blood would NEVER be allowed to join them as “Saints” so Shamrock may have had to claw his way to the top by force with his Haki, skill and determination to not end up a slave like others of his kind. Making himself useful to the point where he could no longer be denied but they will never truly claim him as one of their own.

Shanks mother was a commoner who got pregnant and gave birth to Shanks and Shamrock. This is why their hair color doesn’t match Garling.
Garling must have loved the woman if he acknowledged his sons and did not throw out the mother with the twins from Mary Geoise.
He had given Shanks a chance to return.
Gunko is a halfblood Celestial Dragon who is not recognized by her Celestial Dragon parents and was also a victim of Saturn's experiments like Bonney. She was recruited as a Holy Knight because they were short on recruits. They were trying to recruit Loki
Those of Impure Blood would NEVER be allowed to join them as “Saints” so Shamrock may have had to claw his way to the top by force with his Haki, skill and determination to not end up a slave like others of his kind. Making himself useful to the point where he could no longer be denied but they will never truly claim him as one of their own.