A dispute about fact? Can a tereifah give birth or not?

In Maseches Avodah Zarah, Chullin, and a few other places, there’s a debate about whether a tereifah (an animal with a fatal defect) can give birth. I find this hard to understand — why didn’t they just check this in practice? 

Shalom uVracha,

I have seen a few explanations on this (certainly there are more):

• The Maharshal (Yam Shel Shlomo, Chullin ch. 3) writes that there is a small minority of tereifos that can live and give birth. The dispute is whether this is considered such a negligible minority (mi’uta de-mi’uta) that we need not take it into account, or whether it is a more significant minority that must be considered. (He explains this as the opinion of the Rashba in his responsa; (see his discussion there in detail.)
• The Chasdei David (Tosefta, Kilayim ch. 5) explains that they can give birth, but their offspring do not survive. The dispute is whether this is still considered “giving birth” or not.
• According to the Ran (Chullin 42b), who asks a similar question, even if it seems that the animal does not live or does not give birth, we cannot know whether it is truly impossible in reality for it to live and reproduce, or whether it simply failed to do so because of its weakness.