Hi,
Have you considered getting the birth certs for Lily and James given in reply #1 and reply #10 to see if they match birth dates given in 1939 register entry for couple. One or both may help to confirm if these are yours.
HILTON, LILY - (no mother name listed but reply #3 has her as Hilton born Upholland)
GRO Reference: 1891 M Quarter in WIGAN Volume 08C Page 163
BROWN, JAMES mmn BEECH (This is the only entry for birthdate given and POB)
GRO Reference: 1886 M Quarter in ORMSKIRK Volume 08B Page 862
Also another possibility is the William Beech mentioned as father could be a family member of his mother, as he had no knowledge of his 'Brown' father. It has not been unknown that people did that.
Just a thought
Also in reply #2 Lancs OPC has the father's name as William Beech. (No Grundy)
Can you take a screenshot of father's name from the copy you received from GRO, can then compare to original on Ancestry to see if added? Ancestry has the scanned copy of original.