MySQL 8.0

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Name	ID	Account
Nicole	01	12345
Alexis	02	67890

Name	ID	Account
Nicole	01	991234500
Alexis	02	9912345000
Alexis	02	996789000

SELECT
       CASE WHEN t2.ID IS NULL 
            THEN t1.Name
            ELSE t2.Name
            END Name,
       CASE WHEN t2.ID IS NULL 
            THEN t1.ID
            ELSE t2.ID
            END ID,
       CASE WHEN t2.ID IS NULL 
            THEN t1.Account
            ELSE t2.Account
            END Account,
       CASE WHEN t2.ID IS NULL 
            THEN 'No'
            ELSE 'Yes'
            END Column_A,
       ( SELECT COUNT(t4.Account)
         FROM BankAccounts t4
         WHERE t1.Account = t4.Account ) NumberOfMatches,
       CASE WHEN t2.ID IS NULL 
            THEN CONCAT(t1.Name, ' (OK)')
            ELSE CONCAT(t1.Name, ' (BAD)')
            END Column_B,
       CASE WHEN t2.ID IS NULL 
            THEN NULL
            ELSE t1.ID
            END BadID
FROM Employees t1
LEFT JOIN BankAccounts t2 ON t1.Account LIKE CONCAT('%', t2.Account, '%')
                         AND t1.ID < t2.ID
LEFT JOIN BankAccounts t3 ON t1.Account LIKE CONCAT('%', t3.Account, '%')
                         AND t1.ID > t3.ID
WHERE t3.ID IS NULL
ORDER BY Account, ID;

Name	ID	Account	Column_A	NumberOfMatches	Column_B	BadID
Nicole	01	12345	No	0	Nicole (OK)	null
Alexis	02	67890	No	0	Alexis (OK)	null