I note on the message thread for the 1986 and 1999 games that the last message was posted back in February, nearly three months ago. I don't know if SOM sees that as a lack of interest in single seasons, but I look at it that interest has waned in those particular seasons. Personally, I don't understand what made the 1999 season so special to begin with.
I managed a few teams back when the 1969 season was available, and I thought those leagues filled up somewhat quickly. I enjoyed many of the theme leagues I participated in. Perhaps when 2019 rolls around in three years, SOM can release an updated version of that season. However, in the meantime, how about individual seasons for 1966 (50th anniversary) and 1991 (25th anniversary)??