Previous calculations of surface stress in polyethylene and paraffin crystals are extended to include other experimental and computational data. There are significant changes in the magnitude of the stresses. For polyethylene, these might reflect variations in the nature of the fold surface. Computational modelling yields surface stresses and energies that agree with the experimentally based magnitudes for paraffins but disagree with those for polyethylene. The discrepancy is not reduced by taking account of the effect of neighbouring crystals in the modelling. The agreement of the paraffin modelling results with experiment suggests that the discrepancy for polyethylene has its origins in the model of the fold surface. This raises the possibility that modelling can be used to investigate the nature of the fold surface.