The shortest common superstring problem (SCS) is one of the fundamental optimization problems in the area of data compression and DNA sequencing. The SCS is known to be APX-hard. This paper focuses on the analysis of the approximation ratio of two greedy-based approximation algorithms for it, namely the naive Greedy algorithm and the Group-Merge algorithm. The main results of this paper are:I. We disprove the claim that the input instances of Jiang and Li {JL96} show that the Group-Merge algorithm does not provide any constant approximation for the SCS. We even prove that the Group-Merge algorithm always finds optimal solutions for these instances (except in one trivial case).II. We show that the Greedy algorithm and the Group-Merge algorithm are incomparable according to the approximation ratio.