A doubt about chronology

[Alex13]

Hello,
Today I saw a nice draw of an emblem for the losers' club. However, it said the club was established in 1957.
George Denbrough was killed that year, and the kids fought Pennywise in 1958.
So my quiestion is, in which year was the club established?

 

[GNTLGNT]

....I say 1958.....because as adults they met up again in 1985.....

 

[Karloff]

In 1958, when Mike joined the club after the battle with the Bowers Gang.