In 1956 Lee and Yang proposed parity violation of the weak interactions to explain the $\theta-\tau$ puzzle.
The following year, 1957, Madam Wu and collaborators found that in the $\beta$ decay of Cobalt 60, there was an excess of electrons in the direction opposite to that of the nuclear spin, which was explained by requiring parity violation.
Now, my question is the following: why is it said that the violation is maximal, since in the experiments only the 60% of the electrons and not 100% were emitted in the direction opposite to that of the nuclear spin?
I just can't find anywhere any explanation for this. Isn't it more natural to say that the parity is partially violated and in the standard model lagrangian add a coefficient which encapsulate this asymmetry?