The paper is devoted to model based testing against probabilistic FSMs. Differently from our prior work in 2021, we consider checking sequences and possibilities of test suite minimization through reducing the length of the resulting checking sequence. Given a level of certainty P , we define a P-probably checking sequence under a white box testing assumption and discuss how a suffix of an input sequence can be omitted, such that the resulting sub-sequence is P-probably checking. The specification and possible implementations are non-initialized, i.e., the assumption of 'no reset' is supported.