I experimented with two runs with the same GSFLOW model and compared the results showing different runoff estimates resulting in the upper basin, which doesn't have any lakes or diversions. The two runs are:
(1) using a recent GSFLOW.exe compiled to generate the segments output. The segment output (net depletion) is simulated in MODSIM as static. (Mode: GSFLOW in the control file)
(2) using the coupled MODSIM-GSFLOW code with a MODSIM network that uses iterations and convergence between the two models. (Mode: MODSIM-GSFLOW in the control file)
The comparison of the result of the routed runoff from the upper basin in MODSIM shows the following behavior

and the difference is more notorious in the peak flows.

- the blue line being the GSFLOW mode run.