You almost never need to make an encryption key more than once. If you already have an encryption key for "Medicals," you don't need to make it again.
VSys lists the information that will be encrypted to the right of the field and puts the name of the encryption group in the Key name field.
If you have already made a master encryption key for this type of data, VSys warns you that a master encryption key already exists and that the new key will encrypt all newly saved values with the new master encryption key, but that all existing values will still use the old encryption key. To read older data, you would need to use the older decryption keys and passphrases.
They should be on a USB flash drive or other removable media, not on your hard drive or network drive.
Be sure that you do not lose the master decryption keys or any data encrypted with that key will be gone forever.