That is correct. The only dark star encore was July 13, 1984. According to Deadbase.com (copied and pasted below) there was a shooting star before the dark star was played. It was the first time dark star had been played since 12-31-81.
07-13-84 Greek Theatre, U. of California, Berkeley, Ca. (Fri)
1: Bertha> Greatest, Dire Wolf, C. C. Rider, Loser, Cassidy, Dupree's, Bucket> Might As Well
2: Scarlet> Touch> Fire> Woman Smarter> Drumz> Wheel> Miracle> Stella Blue> Sugar Magnolia E: Dark Star
last "Dark Star": 12-31-81  - shooting star before Dark Star
Ok, another Dark Star Trivia Question (answer may need to wait until Monday).
Only once did the Grateful Dead Play Dark Star as an encore. When and where?
It is rumored that there was a shooting star right before they played that dark star encore.
I believe it was 1984 Greek Theatre in Berkeley in July...I think it was the 13th on the first night of a three night run