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Something like this is almost always used at the very end of the credits creep in movies (and TV shows). But why the cumbersome use of Roman numerals? Why not just say 1998 and be done with it?
According to David Feldman's book Imponderables: The Solution to the Mysteries of Everyday Life:
The general consensus is the "deception theory":
- to "make it difficult for viewers to determine exactly how old the show is", the reason being the older the date the "staler" the material may seem to the audience.
Then there's the "inertia theory":
- That's just the way it's always been done.
This BBC article says something similar:
Perhaps one of the most notable areas where people are likely to come across Roman numerals is in TV and film credits, where the convention is not to spell out what year something was made.
The practice is believed to have started in an attempt to disguise the age of films or television programmes. In other words, the opposite of claiming an undeserved antiquity.
Movies are mostly produced on reels of film (few are digital). Physical film can degrade over time making it difficult to read numeric values. Some numbers will look exactly the same, for example the number 6 will become 5 when the film becomes old. Where as, roman numerals are easier to read when the film degrades. A lot of television shows are also shot with film.
The other problem is languages. Arabic numbers are hard to distinguish in fine print. Two and three look very similar. So the film industry started using roman numerals to ensure the copyright date was always readable.
It's quite often done in order to hide in which year it was created. This way people may think it's older or younger than it actually is.
And as stated above in a previous answer Arabic numbers are hard to distinguish in fine print.
Source: Roman numerals