Pesachim 72: To Err Is Human (But Sometimes, There's No Good Excuse)

The Gemara raises one model of a case, following on the positions of the mishnah,that then is applied to several different halakhic cases. Our case study of this? A case of 2 babies who need brit milah on Shabbat and the day after Shabbat, respectively. Or Friday and Shabbat, in turn. What happens when the wrong baby is circumcised on Shabbat? The outcome is different in those two scenarios, in terms of whether the mohel would be obligated in a korban chatat (and whether the baby is considered circumcised). Along with several other mistaken application of the act he means to do (one being a mistaken sexual encounter, where the intent and the error can result in needing to bring a chatat). Is this boundary-pushing or practical in its acknowledging where people can err? Also: R. Meir's opinion on a non-consecrated animal used for a Korban Pesach - in contrast to a blemished animal, which should be obviously unacceptable for sacrifice, that which is not consecrated is not demonstrably problematic.