This paper reports an analysis of twinning-related phenomena in superalloy PE16 after overaging specimens for up to 100h, whereupon the microstructure is stable against grain growth. The data are compared with other reported statistics on the Sigma3/Sigma3(n) ratio. The ratio shows remarkable stability, with the average Sigma3/Sigma3(n) value being 0.85 in the range 170/o-70%Sigma3s. The explanation for this stability is that either the Sigma3 regeneration mechanism operates, or alternatively impingement reactions are restricted by grain growth suppression due to boundary pinning by gamma-prime precipitates.