No, there have been no alterations of the sort you mention. s127 has received no amendments. And just because an Act is 9 years old doesn't make it "out of date"! Also, the reduction for a guilty plea is not applied (mathematically) post sentencing. See eg s174(2)(d) Criminal Justice Act 2003. 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.