Sometimes, when you look under the chassis, you may find the remnants of the original power cord (with the replacement cord spliced onto it).
Another clue is to consider the date of the radio. My thinking is that cloth-covered cord disappeared in the late-1930s, certainly post-war. Others here may be able to provide a more precise date.
:How is the best way to find out if a radio should have a cloth covered power cord or not? Is there reference material or a general date for the change. Did different brands of radios us different style or color of power cords?