Very interesting discussion. Just a couple of points.
For some reason, it seems that, at least in the earlier part of the 19th century, some (what percentage I wonder?) couples got married several years after their first child(ren) was/were born. Another point, which is somewhat related, is that due to the high mortality rate in the 19th century (and possibly earlier) there may have been instances where the mother (and possibly the father) died at a somewhat young age. The children may then have been taken on by an uncle, for example, and, on marriage, given his name as their father on the marriage certificate. It is therefore essential to check birth and baptismal records to confirm the true father, and even this (knowing(?) our wily old ancestors) cannot necessarily be guaranteed as being 100% accurate. Often, if you descend from an illigitimate line, you take on the family name of the mother rather than the father (who is often unknown) so, in a sense, your grandmother, great-grandmother, or whoever, takes on the roll, as far as family history is concerned, of grandfather or great-grandfather, etc., and you follow her line from thereon back as if it were the unknown paternal line. So, for example, if your illigitimate grandfather's mother's family name was Muggins (with apologies to any Muggins out there!) then you would follow that name back in the mists of time--so, in effect, what you have is a cross-over in the family name. If you are a Muggins then, even if by illigitamacy, you are a Muggins! There's no two ways about it. And, in today's day and age, it is something not to be ashamed of. Lastly, don't forget the struggle that a grandmother, great-grandmother, or whoever, may have had in bringing up (an) illigitimate child/children, even if she was partly culpable!! Charles P.S. There must also be instances, even if rare, of a mother dying young and the widowed husband marrying his late wife's sister and she taking on any children as her own!! Nothing is ever, or hardly ever, straightforward in family history!