Sussex at their best were expected to be good market birds and have hens that were solid layers. No one ever expected mediocrity. Their survival was in the food they raised. They did not have that luxury. There is no good reason why a Sussex pullet should not lay 200 eggs in her first laying cycle, with good management.
Of course there has always been variation between strains and some were better at one than another etc.
Of course there has always been variation between strains and some were better at one than another etc.