To add my two penn'orth:
I have a remot(ish) ancestor who was born in the same quarter as his parents marriage, and is registered under his mother's maiden surname. Either the man she married wasn't his father, or possibly he wasn't present to confirm to the registrar that he was the father. (I haven't got his birth cert, he's a bit too remote for that).
So the son lives with his mother and her husband and the rest of the family - they had a number of other children - but marries under his birth registered surname, and registers his children under that name too. However, in every census, he's shown under the 'family' name of his mother, her husband, and all their children, and once married his wife is also shown with that name.
But when you think of it, the family would have been known under the parents' married name, and therefore the only time the 'official' name for this man would have been required was in formal registration terms - like marriages, births etc.
It seems very likely to me that people would be scrupulous then, but just go with the flow otherwise.
Another example is my OH's grandfather, who was born out of wedlock, but whose mother married soon after his birth, and had another child with her husband. I 'think' it's likely that the husband was the father of OH's grandfather, but haven't been able to prove it. The whole family were then known by the mother's married name.
Come WWI OH's grandfather registers to fight under his mother's married name. However, for some reason - because there were penalties for misinformation? because he was shown his birth certificate? - this is crossed through, and his correct registered birth name is inserted.
And after that - because of 4 years of fighting under his birth registered name, and promotion to lance corporal? - he was known by his birth registered name, as was his whole family (including OH).
But both of his children had his mother's married name as a middle name.