EIA part number codes are an older form of code that indicates the manufacturer, the year of manufacturer and the week of manufacture. For example, 274 was the EIA code for RCA. If you had a capacitor with the following imprint on it:
The number would indicate that the device was made by RCA in 1961 during the sixth week of the year. This was widely employed as a means of quality control, making it possible to figure out who manufactured a component and when.