  In a recent paper [Phys. Rev. Lett. 111, 100501 (2013)], a scheme was
proposed where subsequent observers can extract unambiguous information about
the initial state of a qubit, with finite joint probability of success. Here,
we generalize the problem for arbitrary preparation probabilities (arbitrary
priors). We discuss two different schemes: one where only the joint probability
of success is maximized and another where, in addition, the joint probability
of failure is also minimized. We also derive the mutual information for these
schemes and show that there are some parameter regions for the scheme without
minimizing the joint failure probability where, even though the joint success
probability is maximum, no information is actually transmitted by Alice.
