The L-matrix A s = [1/(n+s)] was introduced in [1]. As a surprising property, we showed that its 2-norm is constant for s ≥ s 0 , where the critical point s 0 is unknown but relies in the interval (1/4, 1/2). In this note, using some delicate calculations we sharpen this result by improving the upper and lower bounds of the interval surrounding s 0 . Moreover, we show that the same property persists for the p-norm of A s matrices. We also obtain the 2-norm of a family of C-matrices with lacunary sequences.