This paper improves the sequential update algorithm proposed in the paper (Masuyama, Queueing Syst., Vol. 92, Nos. 1-2, 2019, pp. 173-200), which computes the stationary distribution vector in continuous-time upper block-Hessenberg Markov chains (upper BHMCs). The original algorithm requires an input parameter set (v, b, C) satisfying both the Foster-Lyapunov drift condition and the convergence condition. Such a parameter set (v, b, C) may not be easy to find in some cases, and the convergence condition does not necessarily hold for any upper BHMC. Furthermore, the original algorithm computes the infinite sums involved with the vector v at each update procedure. These problems are removed from the improved algorithm presented in this paper.