When summing values for each Pop record in SumAll.SumValues where it is calling SumAll.CalculatePlotValues that method is being passed a list of all plots regardless of stratum where it seems like it expecting a list of just plots in the current stratum.
Because of this when Accumulating Stage 1 values ('GrossXPP', 'NetXPP', 'GrossXSP', 'NetXSP'...) are likely higher than they should be because it is including plots from other strata.