There were no non-registered informal informers. all informers had their own file and were registered. 
1950: some 3,000 employees. 1975: 45,000. (as quoted by Bundesbeauftragte für die Unterlagen des Staatssicherheitsdienstes der ehemaligen Deutschen Demokratischen Republik and Bundeszentrale für politische Bildung).This is not 274,00. It is less.
Looking forward to hearing from you
Frogdul