New proofs are given for results by Matthes concerning a certain insensitivity phenomenon displayed, for instance, by many well-known stochastic models from the areas of reliability and telephone engineering.
"Insensitivity of Steady-State Distributions of Generalized Semi-Markov Processes. Part I." Ann. Probab. 5 (1) 87 - 99, February, 1977. https://doi.org/10.1214/aop/1176995893