Dickinson's poems were, for a century or more, snagged in Gordian Knot of copyright restrictions, largely deriving from the fact that Emily's brother, Austin, couldn't keep it in his pants. Several books have been written documenting and trying to untangle the snarl, but basically it is this:
After Emily's death in 1886, her manuscripts were mostly in two hands: her sister Lavinia's and her sister-in-law Susan's — neither of whom liked the other.
Lavinia turned her collection over to Amherst gadfly Mabel Loomis Todd who worked with Boston editor Thomas Wentworth Higginson to "edit" the poems for publication. "Editing" involved reorganizing Emily's words and eccentric punctuation to fit 19th Century conventions, resulting in severely corrupt versions of Emily's originals. These versions, published in a series of three volumes by Roberts Brothers, became the accepted standard, and most cheap or free
Collected Poems of Emily Dickinson, both in print and electronic, are based on these.
Meanwhile, Susan — whose husband had been carrying on a not-too-secret affair with Mabel Todd — refused to contribute her collection to Lavinia's project. Her manuscripts were eventually "edited" and published by Susan's daughter and Emily's niece, Martha Dickinson Bianchi.
The Family Feud of Poetry continued until 1955 when Harvard scholar Thomas H. Johnson gathered the 1,775 known poems, deciphered Emily's tortured handwriting, and Harvard Press published them — chronologically ordered and unedited. This is the basis for the real
Complete Poems of Emily Dickinson.
In 1981, Ralph W. Franklin did what amounts to a forensic study of the various manuscripts and published them, resulting in a different order but not radically different texts.
Scanned (and mostly proofed) copies of the Johnson collection began showing up on the Internet starting with Usnet (remember Usnet?). A few years back, for my own use (legal, since I own bought-and-paid-for dead-tree copies), I made an ebook of the Johnson collection, with a linked index of first lines. If someone can guarantee me that the Johnson texts are public domain (or at least legal for distribution), I'll gladly up my copy.
The
delphiclassics.com collection has an Emily Dickinson volume that contains the Roberts Brothers series as well as what seems to be the 1,775 poems of the Johnson collection (with variorum versions) and the public-domain version of the "Letters." Delphi does a pretty good job on its projects so if you're looking for a cheap ($1.99), probably fairly complete, probably fairly well proofed collection, I'd go with that.