Notes:

Every one of the 11 papers was published after the ICZN invalidated sandrii.
Costa published a redescrition in 1987 (not online).
The ICZN legitimized splendens over sandrii because "CITES used it". The ICZN claims this made use "official". No it did not.
The CITES used the name, once, to delete the names from the list. Recall all Killifish are exempt from CITES and they were trying to remove a name added by mistake.
Thus the name was never used by CITES ever again, and was not really "used" in the traditional sense. It was only used in the context of "oops, this name should not be here. We're removing it.".

I regard L. splendens the junior synonym of L. sandrii.