Pope Stephen V: “That person is a murderer who causes to perish by abortion what has been conceived.”[10]…
So your hypothesis that the Church has a dogmatic teaching that “abortion is murder” is based on only a single sentence which happens to be the personal opinion of a Pope back in 890AD?
Which then happens to be mentioned in a 1974 document from the Vatican, which isn’t developed along the lines you would like, and is written by the CDF without the Pope’s signature.
Surely you can do better than this for a dogmatic teaching?
On the other hand all the heavy weight doctors and theologians of the Church explicitly deny the words of this Pope of 5 years reign and all Popes before and since Pope Stephen V are silent or opposing on this matter.
Strangely, for your thesis, the footnote 10 on the above quote from Pope Steven V refers to Gratian. Gratian is known to deny that abortion is always murder:
Basing his position on writers such as Ivo of Chartres, Augustine, and Jerome, Gratian states: He is not a murderer who brings about abortion before the soul is in the body.
(Gratian, Concordia discordantium canonum, Decretum, Ad. c8, C. XXXII, q. 2.)
So, as a trained scholar, I humbly suggest this means that the quote from Pope Steven V in the CDF document is not placed there to make the point that abortion is murder but rather for another reason as the context suggests.
That the murder theme is not then developed further, and has never been a concern of Popes since 1974 as far as I know suggests you have grasped the wrong end of the stick.
Your “proof” is really no more than amateur “proof texting”.
That is, not much different than just looking for “abortion is murder” in Google and pulling out any vaguely authoritative text that literally says that without judging context.
That is not the professional or scholarly way to approach such matters.
However if you can come back with post 1974 strong Papal support for Pope Steven V against the doctors of the Church and Gratian I am willing to be surprised.
I personally have never come across anything - though there is much in recent Popes to contradict the medieval view on Capital Punishement - but not the medieval view that “abortion is not murder”.