I think that the various ennumerators of the census during the 19c were as casual about names as the users of those names were! within my own family there are variations of spelling although oddly the 'e' spelling was at one time considered the more 'posh' way. I don't know where that idea originated and in any case they were all dockers and 'rock-dodgers' on the ships and barges around severnside. Since Poulain is easily clipped by the local accents I would suggest that the earlier forms probably favour the 'e'. I would like to find some early records from the Somerset area.