The label is discussed by Murray Graham in the June 2002 issue of The Dhow. The translation of the label is:
The Eleventh World Festival
of Youth and Students
The above cover from Mukalla is postmarked 11 December 1977.
The example below from Crater is postmarked 12 February 1978.
I have also seen this cover from Seiyun below postmarked 15 December 1977.