Buffalo Springfield was a Canadian-American rock band active from 1966 to 1968 whose most prominent members were Stephen Stills, Neil Young, and Richie Furay. The band released three albums and several singles, including "For What It's Worth". The band combined elements of folk and country music with British invasion and psychedelic-rock influences, and, along with the Byrds, were part of the early development of folk-rock. With a name taken from a brand of steamroller, Buffalo Springfield formed in Los Angeles in 1966 with Stills (guitar, keyboards, vocals), Dewey Martin (drums, vocals), Bruce Palmer (electric bass), Furay (guitar, vocals), and Young (guitar, harmonica, piano, vocals).

Chris Hillman of the Byrds persuaded the owners of the Whisky a Go Go to give Buffalo Springfield an audition, and they essentially became the house band at the Whisky for seven weeks, from May 2 to June 18, 1966. This series of concerts solidified the band's reputation for live performances and attracted interest from a number of record labels. It also brought an invitation from Friedman to Dickie Davis (who had been the Byrds' lighting manager) to become involved in the group's management. In turn, Davis sought advice from Sonny & Cher's management team, Charlie Greene and Brian Stone; unbeknownst to Davis and Friedman, Greene and Stone then aggressively pitched themselves to the band to be their new managers. Friedman was fired, and Davis was made the group's tour manager. Greene and Stone made a deal with Ahmet Ertegun of Atlantic Records for a four-album contract with a $12,000 advance, following a brief bidding war with Elektra Records and Warner Bros. Records, and arranged for the band to start recording at Gold Star Studios in Hollywood.  The first Buffalo Springfield single, "Nowadays Clancy Can't Even Sing", was released in August, but made little impact outside Los Angeles, where it reached the Top 25. Young and Stills have long maintained that their own mono mix was superior to the stereo mix engineered by Greene and Stone. The band's eponymous album was released by the Atlantic subsidiary Atco in mono and in stereo in December 1966. A revamped version issued both in mono and stereo with a different track order was issued in March of the following year.  In November 1966, Stills composed "For What It's Worth" in response to a protest that had turned into a riot following the closing of a nightclub called Pandora's Box on Sunset Strip. The song was performed on Thanksgiving night at the Whisky a Go Go, recorded within the next few days, and on the air in Los Angeles on radio station KHJ soon afterwards. By March 1967, it was a Top Ten hit. Atco took advantage of this momentum by replacing the song "Baby Don't Scold Me" with "For What It's Worth" and re-releasing the album. "For What It's Worth" sold over one million copies and was awarded a gold disc.,

Using a quote from the above article, answer the following question: When was that released?
in December 1966.