yes sky that was the case apparently, however, the kind of woman who would have that kind of opportunity to make such a protest, though not divided by class or age, may have had a more independant lifestyle than a mother with a family to look after and a husband to fill the census form in.
the 1911 census should tell you the number of children born to the marriage, which would tell you whether the ones you have not found were born before or after the census was taken in the spring of 1911