Supplemental is a subtheme of Universal Building Set that consists of 8 sets that ran from 1969 to 1976. Most sets were released in 1971 which accounted for 5 sets. As of today, the average annual growth of all the sets in Universal Building Set Supplemental is around 4.3% per year. As of today,
990-2 Trees and Signs is the most valuable set in Universal Building Set Supplemental with an estimated new/factory sealed value of $138.98.
LEGO's Universal Building Sets theme was released as early as 1966 but it was not until 1973 that the Basic LEGO sets became known as Universal Building Sets. These sets were produced in two set version numbers, the first was for sets that were sold in the UK, Europe, Canada and Australia. The other version numbers, but for the same exact set with the same box artwork was released in the United States. Most, but not all sets between 1973 and 1981 were sold in both regions.