PLEASE DO NOT POST MY NAME.
you have posted a Q and an A from the ChSofer, pasted below, however the Tosafos YTov explains that Ben Pekuah is a different species which transitions into a Beheimah when it is born but remains a non-Beheima i.e. is a Ben Pekuah when found inside a Kosher to eat mother.
The HAmina is that perhaps even if not found in a Kosher to eat mother, even if it is just not born, it does not transition into a Beheima and wil be a Ben Pekuah.
KaMLan that just having Kalu Lo Chadashav, full gestation and Yatza LeVir HaOlam - that alone determines that it transitions to become a Beheima
The answer of the ChSofer is a little Shver because if the intent of the Mishnah is to define the point at which the Ubbar is Yatza LeAvir HaOlam, it could/should have made that case clearer.
>>INSIGHTS TO THE DAF- CHULIN 74
2) A LIVE CALF FOUND INSIDE A COW THAT WAS NOT SLAUGHTERED
QUESTION: The Mishnah states that when a cow is cut open (without first being properly slaughtered) and a live, nine-month-old calf is found inside it, the calf requires Shechitah in order to be permitted to be eaten, since the mother did not yet have Shechitah.
This seems obvious. What is the Mishnah teaching?
ANSWER: The CHASAM SOFER explains that the Mishnah is discussing a situation in which the mother was cut open while still alive in such a way that its calf is exposed. Even though the mother is then slaughtered with Shechitah, the fetus is no longer permitted through the Shechitah of the mother, since it has become exposed to the world and is no longer concealed within the womb. (Z. Wainstein)<<
1) The Tosfos Yom Tov (4th Perek, Mishnah 5; paragraph in parentheses that starts "Kera'ah") does not in fact write that there is a Havah Amina that even if the mother is not kosher, one still may eat the baby found inside it. Rather, the Tosfos Yom Tov writes that the Havah Amina is that what is found inside the mother is permitted without Shechitah, in the same way as fish do not require Shechitah. However the mother must be of a permitted species in order for there even to be a Havah Amina that what is found inside her is permitted.
2) It appears to me that the Mishnah does hint at what the Chasam Sofer writes. The Mishnah states that the mother was torn open and a 9-month-old baby was present. The baby requires slaughtering because the mother has not been slaughtered. The fact that the Mishnah states that the mother has not yet been slaughtered suggests that she has not yet been slaughtered but will be slaughtered at some later stage. This in turn suggests that the mother is still kosher and was not made a Tereifah by being torn open -- because otherwise Shechitah would be useless on her. So the mother has been torn open but is still kosher. This suggests that the baby is on the way out but is not yet fully out.
Kesivah v'Chasimah Tovah,
Dovid Bloom