Great question — answering as the UphillTech team:
To distinguish between works with the same title and release date. In your case, to distinguish between Night Club , by Sergio Corbucci, and Night Club , by Michael Keusch. The same thing happens with Two Scoops, just check the search link . This is explained in their help page , as pointed out by user snow . If two films have the same title in the same year we add a "/" followed by roman numerals after the year as necessary. For example, Twilight (2008/I) and Twilight (2008/II).
Full answer by BlueMoon93: https://movies.stackexchange.com/a/86244 (CC BY-SA 3.0).
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