This is both inadequate and irrelevant. I asked for specific citations to support your specific claim that "There are many statements that say the death penalty must (or must not) be used to defend the common good."
Every part is directed to the whole, as imperfect to perfect, wherefore every part exists naturally for the sake of the whole. For this reason we see that if the health of the whole human body demands the excision of a member, because it became putrid or infectious to the other members, it would be both praiseworthy and healthful to have it cut away. Now every individual person is related to the entire society as a part to the whole. Therefore if a man be dangerous and infectious to the community, on account of some sin, it is praiseworthy and healthful that he be killed in order to safeguard the common good, since "a little leaven corrupteth the whole lump” (1 Cor. 5:6).
(Summa Theologiae, II, II, q. 64, art. 2)
From the point of view of our faith, no one ought to slay a person who in the course of nature still would have time for repentance up to the very moment of his death. A guilty man provided a premature punishment had not deprived him of life could well procure forgiveness by redeeming himself by an act of repentance, however belated. (St. Ambrose, Cain and Abel, II.7.38)
The public authority is given the power to kill wrongdoers, and that not unjustly, since it is necessary for the defense of the commonwealth. (St. Alphonsus Liguori)
Do not condemn to death, and there will be someone there who can repent. Do not have a person put to death and you will have someone who can be reformed. As a man having this kind of love for men in your heart, be a judge of the earth. Love terrifying them if you like, but still go on loving. I don’t deny that penalties must be applied. I don’t forbid it. But let it be done in a spirit of love a spirit of caring, a spirit of reforming. (St. Augustine)
For, although we can deny any responsibility for the death of those who are seen to have been handed over for judgment, not due to the accusations of ours, but because of the indictment of those who have charge of the defense of the public peace, we still do not want the sufferings of the servants of God to be avenged by punishments equal to those sufferings, as by the law requiring an eye for an eye. (St. Augustine)
Except in the case of the definition of the Traditional teaching on capital punishment where the two versions are strikingly different.
Also from the same Apostolic Letter:
Catechesis will find in this genuine, systematic presentation of the faith and of Catholic doctrine a
totally reliable way to present, with renewed fervor,
each and every part of the Christian message to the people of our time. (bold mine)
There isn’t made an exception for what the Catechism says on the death penalty.
Cardinal Ratzinger’s comments:
It is not therefore a new Catechism, but only the final text of the Latin Catechism of the Catholic Church, which since 1992 has already been translated and published in about thirty languages, and are about a dozen in the course of preparation. In this Latin typical edition will have to comply now all translations, **even those already published. ** (Bold mine)
vatican.va/roman_curia/congregations/cfaith/documents/rc_con_cfaith_doc_09091997_cathechism_it.html
And these are the people who were part of the Interdicasterial Commission for the Catechism: Ratzinger, Card. Schotte, Bertone, Schonborn, Ternyák Csaba, and Claudio Maria Celli.