I fear replying may be all I can do! The census information is useful to confirm birth location.
But then again - I started looking at the LDS library to see what records they had for Castor - they often have many records not transcribed on the IGI - I discovered that the IGI information was from parish records - rather than BTs which often have records missing. The good site of hugh Wallis
http://freepages.genealogy.rootsweb.com/~hughwallis/IGIBatchNumbers.htm#Menugives the batch number for births - P016811 and using that batch searched for Alice (no surname) and found this one
ALICE CULPIN Christening: 28 DEC 1794 Castor, Northampton, England
Father: WM. CULPIN Mother: MARY
It is an extracted IGI record - what do you think?
Trish
Edit: There are some siblings in the batch as well - sadly it stops at 1800 - there are probably more.