For artists tossed to the sidelines by tunnel-visioned major labels, freedom may await. We hear about the personal and professional suffering veterans endure in such situations, but there can be beauty and artistry on the margins — at least for those not broken by the rejection. Aged out of “contemporary” country relevance, Dolly Parton retrenched into her roots and produced a trilogy of sublime bluegrass recordings: The Grass Is Blue (1999), Little Sparrow (2001) and Halos & Horns (2002). Filled with banjo, mandolin, sparkling harmonies and inspired covers (“I Get a Kick Out of You,” “Stairway to Heaven”), they represent an enviable winning streak. And all the material’s collected here with a bonus DVD that includes new mixes of five songs, three music videos and footage of Dolly performing a duet of “The Grass Is Blue” with Norah Jones. Gorgeous stuff.