Since I lack in - depth knowledge of the Clarence Day collection novels, it's difficult to say for sure. However, if Clarence Day has a distinct voice as an author, the novels in the collection might be characterized by his unique use of language, his way of developing characters, and his exploration of certain cultural or social aspects. Maybe his novels often take place in a particular setting, like a small town or a big city, which could be a recurring characteristic. Also, the themes could range from love and loss to the search for identity. Without reading them, this is all speculation though.
I'm not sure precisely as I don't know this collection well. But perhaps they might share a common writing style or theme related to the author's perspective or the era in which they were written.
Not having studied the Clarence Day collection novels closely, we can only make some educated guesses about their characteristics. If Day was influenced by the literary trends of his time, the novels might have elements of the prevalent literary movements. For example, if it was during a time of realism, the novels could be very detailed in their descriptions of daily life and the social fabric. They might also have a particular tone, whether it be humorous, melancholic or something else. And depending on Day's own beliefs and experiences, there could be recurring moral or philosophical undertones in the novels.