Just purchased an IBM Model 11C (per the manufacturers tag). When attempting to decode the serial number for the production year at the typewriter database, appears that this is classed as just a model C but the serial number of 209795 did not seem to match the format. Noted that my machine has the ribbon spools mounted vertically, whereas the models in the database have them mounted horizontally. I believe this to be one of the machines produced in the late 50's. There also seems to be possibly 2 letters (DD - possibly for Department of Defense??) added before the serial number at some time. There is a service tag affixed to the underside front that identifies this as a Model 11 with the serial number of 209795. I would appreciate any info for clarification.