struct NSSCMSKeyAgreeRecipientInfoStr {
    SECItem version;
    NSSCMSOriginatorIdentifierOrKey originatorIdentifierOrKey;
    SECItem *ukm; /* optional */  // <- a pointer
    SECAlgorithmID keyEncAlg;
    NSSCMSRecipientEncryptedKey **recipientEncryptedKeys;
};

struct NSSCMSKeyAgreeRecipientInfoStr {
    SECItem version;
    NSSCMSOriginatorIdentifierOrKey originatorIdentifierOrKey;
    SECItem ukm; /* optional */  // <- it's a value now, growing in size
    SECAlgorithmID keyEncAlg;
    NSSCMSRecipientEncryptedKey **recipientEncryptedKeys;
};
typedef struct NSSCMSKeyAgreeRecipientInfoStr NSSCMSKeyAgreeRecipientInfo;

struct NSSCMSRecipientInfoStr {  // <- changes size as well
    NSSCMSRecipientInfoIDSelector recipientInfoType;
    union {  // <- could've dampened the size change, but no, the growing member is the largest one
        NSSCMSKeyTransRecipientInfo keyTransRecipientInfo;
        NSSCMSKeyAgreeRecipientInfo keyAgreeRecipientInfo;  // <- here's the growing struct
        NSSCMSKEKRecipientInfo kekRecipientInfo;
        NSSCMSKeyTransRecipientInfoEx keyTransRecipientInfoEx;
    } ri;
    /* --------- local; not part of encoding --------- */
    NSSCMSMessage *cmsg;   /* back pointer to message */  // <- offset changes
    CERTCertificate *cert; /* recipient's certificate */  // <- offset changes
};
typedef struct NSSCMSRecipientInfoStr NSSCMSRecipientInfo;

struct NSSCMSEnvelopedDataStr { ... NSSCMSRecipientInfo **recipientInfos;  ... };
typedef struct NSSCMSEnvelopedDataStr NSSCMSEnvelopedData;