What we have here would by all accounts be the earliest R.E.M. recording that is known in existence.  This recording came via a trader who had obtained the tape back in the days when "Tape Trading" meant exactly that, a method to take cassette tapes and trade them. 
 
What we know. The tape itself was labeled "R.E.M 1980" which while tapes are frequently incorrect so we cannot go by the tape information itself. 
 
Secondly, during the tape, Michael promoted a "Side Effects" show on June 4th. Based on the setlist below, the only two possible years that this tape could have come from would be either 1980 or 1981 either in early June or in most cases late May. 
 
Third, R.E.M. did play on June 4th, 1981 at Tyrones, O.C., which would mean that either it was a double-bill or a weird way to promote another band, albeit close one by promoting them vs. themselves.
 
Last, the setlist itself contains several early tracks which never make an appearance anywhere else. Tracks such as Chappaquiddick,  Mediocrity, and I've Got a Charm, appear to be a handful that are not found anywhere in 1981. The vocal stylings, especially of Mike Mills would also lead you to believe that the band was still in it's infancy during this recording. 
Now the band had played a show on May 30th at the 40 Watt Club, however, according to Paul Butchart, both of the Side Effects and an Athens Music Historian, the 40 Watt did not have recording equipment possible to make this recording. Suffice to say, most fans are stumped. 
 
In terms of trying to keep things neat and tidy, most sites list this date as the shows date unless any data would prove otherwise. I believe 100% that the show took place sometime in May of 1980, and it could be possible that a show was missed or not promoted in the local newspapers as the reason for a true date not appearing. I would also suggest that based on the comments by Michael above about the Side Effects show was that the concert did not happen at Tyrones, but a different club in Athens. 
 
This is a true artifact. The three songs I mentioned above all make this recording very unique. They also performed covers of Route 66 and Johnny Kidd and the Pirates Shakin All Over, the latter also never appearing on any R.E.M. recording. 
 
A special thanks to Jonathan Moore for resurrecting this show and posting it to the public for everyone to enjoy. Truth be told, that moment almost never occurred when the tape broke while playing it back. Jonathan was able enough to tape it back together and make a recording out of it. 
 
Tracks (Right Click to Download)
1.  Baby I
2.  Route 66
3.  Sheherazade
4.  Lisa Says / Mystery To Me
5.  Chappaquiddick
6.  All the Right Friends
7.  A Girl Like You
8.  Dangerous Times
9.  Mediocrity
10.  Shakin All Over
11. I've Got a Charm
12. Bodycount
13. Different Girl