Thanks to all who have taken the trouble to respond. You have at least confirmed that I have not missed anything obvious.
Maddys52 has correctly identified Emma's family and census references.
I am satisfied that this is "my" Emma. Only two children were registered in the name of Emma Greening in Devon between 1837/55 and the other one died in infancy. An Emma Jane Greening married in Stoke Damerel in 1865 was born in Dorset.
I have checked GRO Index for Curtis/Greening births post 1869 and drawn a blank, which encourages me to conclude they left the country. Does anyone know is it possible to search Curt* and Court* to cover the possibility of variation?
I recognise the potential value of the information contained in the marriage certificate but am not convinced that any additional detail about Samuel is going to add much in the forward search for them. If no further progress is made then I shall have to pursue that course.