Agreed those SAR figures are conservative as more often than not strong HWCs and ISA+ temps push up the final SGR figures.
I've also found detailed track averaging too cumbersome and liable to mistakes under exam pressure conditons. Basically eyeballing the RSWT against the ERC-H waypoints produces a very near result in many cases.
Also regarding fuel allowances they often switch between startup weight and BRW - one of the many annoyances to get you wandering further off the correct answer.