To further expand on Ford's use of part's numbering; engineering part numbers may or may not have a suffix, the first design/option was blank, the second variation was a "-B"; service part numbers usually have a suffix even if there is only one version, "-A". Ford, from an engineering standpoint, had a workable system for designing, part production and assembly line use although it was occasionally not followed. We, at Ford Aerospace, referred to the parent company's practices as - "creative part number engineering", they did almost what ever they wanted to do. Service part numbers were more formal and "controlled" better.
Jim