This paper shows the Unique Input/Output, UIO, approach and the Distinguishing Sequence, DS, approach for the conformance testing of protocol implementations do not always produce identical fault converges, contrary to a previous claim. In the UIO approach, when UIO sequences and signatures are not unique in an implementation, they may not be able to detect erroneous states in the implementation. The UIO approach is revised here with the addition of a verification procedure to ensure that the UIO sequences are all unique in an implementation. Since signatures are generally not unique, this revision requires substituting the use of a signature for a state, S, with a set of input/output sequences, IO(S,K)s, unique to S, each of which distinguishes S from at least one other state, K. Verification is then applied to the IO(S,K)s. Fault coverage in the revised UIO, UIOv, approach is better than that in the original approach. A uniqueness criterion is discussed here to capture a desirable fault coverage for finite-state machine, FSM, test sequences. This criterion ensures the detection of any faulty FSM implementation provided that its set of states does not exceed that in the specified FSM. It is shown that test sequences generated by the UIOv approach and the DS approach always satisfy the uniqueness criterion. In fact, the DS approach is a special case of the UIOv approach; however, the UIOv approach has wider applicability and is generally applicable to k-distinguishable FSMs.