I’m referring to one of the reasons a woman bring such a korban after birth of a child.
Yes, but the truth is that the reasoning for that is not absolute. One brings a korban chatas after childbirth, even if no such sh’vua was made or even if no such sh’vua could have been made (for example, if the mother was in a coma).
The bottom line is that a chatas is brought after childbirth for reasons that, ultimately, are known only to HKBH. We may try to come up with post-hoc reasonings (such as the one you bring), but you cannot rely on them to make halachic rulings in other areas (such as with chametz in your car).
The Wolf