It is very difficult to decide whether a small book is an impression, defined as a new printing of an existing edition, or it's a new edition, a book that has been revised in its content. Carr often reprinted his small books with a new cover and made small changes to the text inside the front or rear cover but kept the same poems; or he kept the covers the same and changed the poems or their order within. I have tended to use the term impressions for the small books unless there was a change in both covers and contents, such as the two versions of Lord Byron. But I'm probably not consistent.