no there have been no alterations of the sort you mention s has received no amendments and just because an act is years old doesn't make it out of date also the reduction for a guilty plea is not applied mathematically post sentencing see eg s d criminal justice act the process begins with the court deciding the sentence that should be imposed for the offence s then selects the amount of the reduction by reference to the sliding scale then applies the reduction and finally pronounces sentence in court explaining what reductions were applied