Ray,
Sorry, must dash- off to one of my other passions- Racing at Sedgefield
Have a look at 1881 census (page ref 5115-82-23, a candidate for that Margaret J, ten years after..... ages, occupation ok, Robert and Margaret J birth places don't tally , but ??
There is a candidate for a Margaret Clark 1868 in both Tynemouth ( for Seaton Delaval) and Morpeth ( for Bedlington)
Also marriage reg Dec 1867 Morpeth.. Robert Clark marrying ( very likely ? ) Mary MILLER.... did you spot the two sibling-in-laws called Miller on the 1871 census.
What is needed is finding both a Jane and Margaret J on same census to accept that they are two different people... or vice versa..
Later
Michael