I looked up the study, and it seems that participants were not allowed to use a second method of birth control:
"Couples enrolled in the efficacy phase were asked to rely only on these injections for contraception."
And there were four pregnancies during the study (from the abstract of the study):
During the efficacy phase of up to 56 weeks, 4 pregnancies occurred
among the partners of the 266 male participants, with the rate of 1.57 per 100 continuing users
(95% CI, 0.59 – 4.14)
I don't think they were measuring the efficacy on the basis of whether or not the participants conceived - that measure is affected by too many variables. Sperm count is the more reliable metric with reasonable granularity for measuring the effect.
"Couples enrolled in the efficacy phase were asked to rely only on these injections for contraception."
And there were four pregnancies during the study (from the abstract of the study):
During the efficacy phase of up to 56 weeks, 4 pregnancies occurred among the partners of the 266 male participants, with the rate of 1.57 per 100 continuing users (95% CI, 0.59 – 4.14)