There are two different error messages for adding duplicate record to CS by same command.

/subsystem=elytron/credential-store=cs007:add(uri="cr-store://test/customcredCS007.jceks?create.storage=true", credential-reference={clear-text=pass123})

/subsystem=elytron/credential-store=cs007/alias=alias001:add(secret-value=secret)

/subsystem=elytron/credential-store=cs007/alias=alias001:add(secret-value=secret)
{
    "outcome" => "failed",
    "failure-description" => "WFLYCTL0212: Duplicate resource [
    (\"subsystem\" => \"elytron\"),
    (\"credential-store\" => \"cs007\"),
    (\"alias\" => \"alias001\")
]",
    "rolled-back" => true
}

/subsystem=elytron/credential-store=cs007/alias=ALIAS001:add(secret-value=secret)
{
    "outcome" => "failed",
    "failure-description" => "WFLYELY00913: Credential alias \"alias001\" of credential type \"org.wildfly.security.credential.PasswordCredential\" already exists in the store",
    "rolled-back" => true
}