We haven't been able to reproduce the 599 either but I'll check with the Institute to see whether they still have the workings behind this and, if so, I'll post the answer here. In an exam, any reasonable method or set of assumptions would get the marks so don't worry too much about this one number.
The 599 in the reserve calculation is the inflation-adjusted (to 2004) average cost for the years 1998 to 2001 inclusive. The calculation is (275.0 + 749.7 + 252.5 + 1118.9) / 4 = 599.0 I hope that helps.
