Sorry that things do not appear to be correct.
I suppose Vin's first wife (Jane) was the one who died in Retford in 1855.
You didn't say if the bride in the Grantham marriage was Ann CLARK, nor did you mention whether Vin's father had the right name, or whether the occupation was correct.
However ... with respect to the identity of your Vin's wife Ann, I feel I must point out that in the 1851 census there was
Swinegate, Grantham
Ann CLARK (unm) 30 Gen Servant, Lincs Broughton ...
which seems a pretty close match to me.
It seems you have two courses of action available to you-
1) Accept that your certificate - a transcription - contains an error regarding Vin's marital status.
2) Reject the certificate meaning you need to find (to set your mind at rest)...
i) another Vin FLETCHER with the right father's name who could have married Ann CLARK
ii) another Ann from Broughton born c1823 who could have married Vin FLETCHER
iii) find Ann CLARK on the 1861 census to discover her fate
and probably other things as well.
At the end of the day, you have to set your own level of proof.