As we continue to celebrate the anniversary of the publication of Robert Frost’s 1923 book, “New  Hampshire,” it makes sense to turn at least some of our attention to standout poems from collections that preceded it. As early as 1914, with the publication of “North of Boston,” when he was 40, Frost was beginning to write what in hindsight we think of as such quintessentially “Robert Frost poems” as “Mending Wall” and “The Death of the Hired Man.” The 1916 volume “Mountain Interval,” meanwhile, following fast on the heels of the previous book, continued to reflect the poet’s voice as it matured and more fully realized itself.