Because there is the description of '因還信' (delivered by a messenger) in the second letter and '因還人' (delivered by a messenger) in the third letter, it is presumed that each letter was written casually (with no intention of creating artwork).
2通目の文中に「因還信」、3通目に「因還人」とある所からみて、それぞれ率意の書であるとも思われる。