purchase [Heart of Gold]
Sad disclosure to apologize for the quality of my research: Turkey continues to block Wikipedia - limiting my ability to access further steps related to my ideas. (It needs to be said)
Crosby, Stills and Nash came out with their first album at the end of the 60s. A veritable powerhouse/Supergroup that included some of the best from Bufallo Springfield, the Byrds ... the top of the charts. (And as JDavid just said, they had their personality problems.)
The album [link] they came out with in '69 includes a collection of rock classics: Suite: Judy Blue Eyes, Marrakesh Express, Guinevere,Wooden Ships, Helplessly Hoping, Long Time Gone. Heck .. they're all good. The collaboration lead them to Woodstock. No small feat.
It appears that it was Ahmet Ertegun (back once again to Turkey!) who convinced CSN that another Atlantic artist by the name of Neil Young might fit in with the original 3. It wasn't exactly a smooth transition, but ... the result was historical: CSNY.
Neil Young brought in an element of edgy-ness, and probably some additional discord in the process: it's hard enough to get 3 musicians aligned. Adding one more only exacerbates the issues. But the roughness of Young's style took the group to a new level and arguably maintained, if not increased their appeal. Thankfully, they managed to hold it together for longer than most people predicted, and we ended up with Deja Vu and 4 Way Street as they helped lead the political voice of America into the 70's.
In '71, Neil Young came out with Harvest - another rock classic that includes Old Man, The Needle and the Damage Done and Heart of Gold. The album was panned by critics but the public was of another mind - one of his most successful works to this day.
Further disclosure: 2-3 years back our blogger Andy LaRayGun, some friends and I did a Neil Young cover at about this time of year in front of maybe 500 students. Andy on the left, me next to him (black guitar doing the vocals)