A title can hold a moving text
Asking what Leaves of Grass says is a little like asking what a city looks like without giving a year. There is a recognizable identity, but the details depend on the moment. The analogy matters when a quotation or an argument quietly moves between editions.
The Library of Congress describes a progression from twelve poems in the 1855 edition to almost four hundred by the 1891–1892 edition. Whitman added poems, changed titles, regrouped material and altered language and punctuation. These were changes within a continuing project, not merely fresh covers around an identical text.
Sources: s1
Drafts reveal a different kind of evidence
The Library's Charles E. Feinberg collection includes drafts, notes and corrected proofs. Such material can show an act of revision that a finished volume conceals. It supports a question about how a line developed, while a particular published edition supports a question about what readers could encounter in that edition.
Begin a comparison with two identified texts. Record edition, publication date, poem title and the location of the passage. Then describe the actual difference: an added word, a moved section, a changed title. Only after establishing that difference should an interpretation explain what it might do to voice or meaning.
The gap between change and motive
A revision can demonstrate that wording changed. It does not, by itself, tell us every reason Whitman changed it or how every reader responded. Letters, notes and reception evidence may help with those questions. Keeping the textual observation visible lets readers assess an interpretation without confusing it with the fact on which it rests.