Thank you. I didn't know that about Handsworth so thanks. I'm leaning towards illegitimacy as I can't find a record for John Southall (other than Stourbridge which is not my Nellie) . Dead end then thoughThe birth, marriage and 1901 census I posted all point to the Nellie you found with Mary J on the 1891 NOT being the one you want.
Remember in 1890s to early 1900s Handsworth came under Staffordshire with births reg in West Bromwich.
I think either her Father was John or she was illegitimate and gave that name to save face.