The base dates used are 16 August 16, 1995 (SET50 Index) and 30 April 2005 (SET100 Index), which are the respective dates that the two indices were first published and were set to a base value of 1000 points.
The provided text describes the starting values used to calculate the SET50 and SET100 indices. The dates August 16, 1995, and April 30, 2005, are significant as they mark the first publication of each index with a base value of 1000 points.