This is to allow the processing program to distinguish these locations from sole practitioners. The dummy accts are not included in the data files. A town is always within a single csd, but a csd may include any number of towns. Typically a town is the only town in a csd, and has the same name as the csd. The file csd90 is a complete list of towns, and the csds they belong to in 1990.
Towns appear by name, csds by cd code and csd code.
Some single csds in 1990 were formerly several csds. And so on, by analogy.