The law matters in genealogical research. Many genealogical conclusions and research approaches are based upon what laws were in effect when our ancestors were living in a certain time and place.
There are those occasional times when the law is ignored for one reason or another. But before you decide your ancestor (or your family) was ignoring or skirting the law, ask yourself, “how plausible is it that my ancestor could get away with this?”
It’s one thing to get married a few years before being of legal age. It’s possible, but perhaps slightly more difficult, to marry when you’ve got a spouse and five children living in the same county where you are marrying again. It’s difficult to leave two siblings out of your parent’s estate when they died intestate and live in the same county (it’s one thing to abscond with some of mother’s good china, it’s more difficult to sell the farm in an intestate probate without getting all the heirs to sign off on the deed).
It’s one thing to make illegal moonshine for thirty years. It’s another to get a military pension when you did not serve or were a “widow” who was not married to the veteran.
Before you think your ancestor skirted the law, give a hard think to how easy it was to do that.