= Solution
In the final data, the only deaths by treatment duration twelve are B and E. Thus
$$
\widehat F_\infty(12)=\frac23.
$$
The month-24 estimate already has this numerical value, so month 24 is the first twelve-monthly analysis satisfying $\widehat F_M(12)=\widehat F_\infty(12)$.
Equality is not yet knowable at month 24 because patient F has only nine months of follow-up and could still die before duration twelve. Patient F reaches twelve complete months at the end of month 27, so month 36 is the earliest scheduled analysis at which the final value at duration twelve is evaluable.
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