Actually, there were fact-checkers way back then. They were the various priests and orders of the Catholic Church. And, much like the modern era’s inquisitors of the leftists’ self-proclaimed Magisterium, they brooked no dissent or deviation from the orthodoxy that they had created. Thankfully, so far, the Left has settled for censorship and destruction of property, whereas the Church put heretics down, often brutally and only after extensive physical torment.
In truth though, the only functional difference between the fact-checkers of the past and the ones of today is how their taskmasters respond to findings of heretical “misinformation.”