Returning to the Flagrant Vandals made Ves experience the deplorable level of technology that was the norm in much of the galactic rim.
The Shield of Hispania's medical bay lacked the high technology medical equipment that could make sense of his altered physiology. Their doctors also didn't recognize the effects of gene optimization treatment.
Since their medical examination failed to confirm the identities of Ves and Captain Orfan, the Vandals resorted to an alternative method.
They first put them through various cognitive and emotional tests to see whether their current behavior matched their known behavior.
Then they brought in various Vandal servicemen they were familiar with to have a chat. Usually, a friend who interacted a lot with someone would know if that person got replaced by a clone. While clones were able to emulate the behavior of their originals to a superficial level, they often dropped the ball during longer and deeper conversations.