Have you looked for Goodfellow births in the right area after 1911?
In theory your couple could still have had children that perhaps died young. Realise it will be hard to prove the right parents without certificates but if there were any with similar names could be worth following up.
Only 8 Goodfellows registered in Maidenhead from 1911-1921, 3 of them are children of Magnus Goodfellow and Margaret A Woolfenden, and the other 4 are children of Arthur Goodfellow and Daisy Reeves (my 2x great grandparents! So already accounted for

) the final is a daughter of Harry Goodfellow and Annie Cottrell. 1921 Census also says Alfred & Hettie had no minor dependents at the time, so very likely no children!
1939 Reg says she was born in Windsor 29 June 1878,
It doesn't show birth places in 1939 does it?
There's a Hetty Maria Davis baptised in Burbage Wilts 8 Sep 1878.
Birth reg under Henrietta Maria. No ancestry hints for her after 1891.
Apologies you're right, the censuses list her pob as Windsor but the 39 Reg her dob. I will have a nosy at Hetty Maria Davis though, thank you!
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Thank you for all your mind-bending hard work today John! So sorry for sending you down such a tough rabbit hole. Wouldn't be the first time there's a bigamous marriage amongst the Goodfellows lol, do let me know what else you come up with as it may be worth having a look!
Ali