Both Nightmare on Elm Street and Friday the 13th had flawed premises. Though Friday the 13th got the seeds of my genios,* which is,

Why could they not start with Nightmare on #1 Elm Street, and call the sequels #3 Elm Street, #5 Elm Street, and so on, until they got to the end of the street, then come back on the other side, counting down the even numbered addresses.

Similarly, Friday the 13th could have had a sequel "Friday the 14th", "Friday the 15th" and so on.

If the direction and the producers had been budget-conscious, they could have more than doubled the theoretically possible number of sequels by starting with "Friday the 1st."

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* Not a typo. I am not a genius, and you don't have to be either, to realize that I got two large genios in the inside bend of my left elbow.

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Thinking along, don't you guys agree, that "Friday the 13th II", "Friday the Thirteenth III",... "Friday the 13th MCMLXXXVII", etc. sound ridiculous? The only people who'd see any artistic merit in that would be librarians who are absolutely crazy about the Dewie decimal system.