Something I just thought of, as a side thought. When birthcontrol fails for women (assuming something like a shot that is controlled by a doctor) you 100% know that the failure was a result of the contraceptive. But for men you can't be sure, it's possible that some of those pregnancies were the result of their partners being unfaithful, so the injection might be better then the study shows.

So when you look at something cynical like sperm count/eggs released vs. real world results that could be a factor. according to 2 minutes of google 19.2% of women indicated that they had "cheated" during their current relationship. So there is a fair chance that one of those pregnancies was due to that. Of course that's just based on a statistic, it could easily be all or none of them, but it's something that would have to be considered when looking at a sample size like this. Once there are thousands of participants in either studies or real world results we might be a better idea, because right now a sample of 4 could be swung hugly by cheating.