So I went to work on it. My guess was that, like much else with Google books, the data was ratty. It didn’t have to look far. At first glance this chart appears to show that “fuck” had a remarkable early history—being more popular in 1725 than even today! (link)
Yes, Google can’t tell between an f and an ſ, the “s without a bar” more properly known as a long, descending or medial s. To the disappointment of many, Shakespeare wrote “suck’d.” The effect pops up all over. Here’s a graph of “crimſon” vs. “crimson.” If nothing else we can now follow the demise of the ſ with precision.
There’s no question this is a cool tool. But given Google’s grand ambitions and how common s is in English, it’s a pretty startling lapse.