I hadn't considered incest as a possibility, because at that time there were just so many people with the same surname. In fact in Scotland there is sometimes said to have been a tendency for people to change their surname if they moved to the area of a different clan, but I've never looked into this in detail - and as there are very few written records when you get that far back, it would be very hard to prove (or disprove).
Over here you will sometimes come across cousin marriages, even first cousins, whereas I understand that some states in the US forbid them - and would they be classed as incest? Sometimes an eyebrow might be raised for first cousins, but it's never been illegal. Having said that, Roman Catholic marriage registers record that special permission is given when cousins wish to marry, and I don't know if they would give it for first cousins, but that's a church rule, not the law of the land.
Finding a case of actual incest as understood here is quite unusual, but I couldn't say whether that's because it was hushed up or because the penalties were so severe as to be an effective deterrent.