I have an Fed-1 (C) NKVD with serial number 56450 (1937/1939). Following the indications of sovietcams.com, determined by serial number, the camera is of the PE0225 type. The detail that escapes me is that this model should have small bolt - bottom plate holder.
Conversely mine has bigger bolt - bottom plate holder ! Always following sovietcams.com those with the bigger bolt,should be between serial numbers 80.000-87.000 about.
Ask how it is possible ? Thanks a lot. Luigi from Italy