From 1990 until 1994 the calendars where published by Ballentines, with one exception of 1991 when there was also a Allen and Unwin edition. this was also the last calendar published by Allen and Unwin. From 1995 the publishign of the calendars was taken over by Harper Collins, who published the yearly Tolkien calendars from then on.
1992 was a special year, celebrating 100 years of Tolkien. Therefor a special celebration edition was published.