My search for John & Charlotte Crisp in the 1871 census turned up negative but thanks to RootsChat their children were found living with an aunt, Mary Ann Tainby and several of her children living in London.
I was pleased to have found another relative & searched high & low for her, trying various combinations, Toynbee included, but without success.
Then the other day I looked again at the original printout and thought... could it be... yes it might just be... Lumley! John Crisp's wife's maiden name was Lumley! Couldn't find Mary Ann Lumley in the 1881 census but have found one of her children which verified the name.
However using the free trial I was looking for Derrets in Gloucestershire and some names were listed that I couldn't find at first glance on the original. A William J Derrett was listed as son. I then realised it should have been listed as William J Cole, Head. This entry was the next one under the Derrets! If some poor soul looks for him he would certainly prove difficult to find. Would YOU look up Derrett if you were looking for Cole?
You could try looking for all the Sarah's born in Plymouth. If there are too many then you could try 1818, then 1817, then 1819 etc. Rather labourious but something may stand out.
Having said that I still can't find my Leahy's in the 1901 census. They had lots of children including a Patrick, Cornelius, Kathleen, Francis, Bernard etc but can I find them.....................NO!