The 3-parameter logistic (3PL) model including guessing parameters is one of the popular models in item response theory. While the guessing parameters in the fixed-effects 3PL model with non-stochastic abilities have been believed to have identification, some counter examples with new ones given in this paper are currently available. In this paper, the concept of degeneracy for nested models is introduced. Some degenerate cases in the counter examples are shown to have model identification for guessing parameters, which are further shown to have model unidentification in a more degenerate model. Similar results in the fixed-effects 4-parameter logistic model are also derived.