Hi again anonymous, You mention the BMD in your reasoning but not the censuses so I guess that you may not have them so below are those for Lucy after her marriage. As you can see, although the names vary slightly she always seems to be reporting her birth as the local Wooldale area, which leads me to another strategy for isolating info about her birth but more of that in comments below the census returns...
1871 Census...
CASTLE, John Head M 24 1847 Kirkburton,Yorkshire
CASTLE, Lucy Wife F 19 1852 Kirkburton,Yorkshire
CASTLE, Hugh Son M 0 1871 Kirkburton,Yorkshire
CASTLE, John Grandfather M 68 1803 Kirkburton,Yorkshire
Piece: 4350 Folio: 60 Page: 12 Registration District: Huddersfield
Civil Parish: Wooldale Address: Water Row New Mill, Wooldale County: Yorkshire
1881 Census...
CASTLE, John Head Married M 34 1847 Worsted Weaver Fulstone, Yorkshire
CASTLE, Lucy Wife Married F 29 1852 Holmfirth, Yorkshire
CASTLE, Hugh Son Single M 11 1870 Scholar Wooldale, Yorkshire
CASTLE, Frederick W Son Single M 9 1872 Scholar Wooldale, Yorkshire
CASTLE, Sam Son Single M 7 1874 Scholar Wooldale, Yorkshire
CASTLE, Annie Daughter Single F 4 1877 Scholar Wooldale, Yorkshire
CASTLE, Luther Son Single M 2 1879 Wooldale, Yorkshire
CASTLE, Harriet Daughter Single F 0 1881 Wooldale, Yorkshire
Piece: 4372 Folio: 77 Page: 14 Registration District: Huddersfield
Civil Parish: Wooldale Address: Fearnley Lane, Wooldale County: Yorkshire (West riding)