Hm there is a lot of text from before the internet, but most of it is not on internet. There is a weird gap in some circles because of that, people are rediscovering work from pre 1980s researchers that only exist in books that have never been re-edited and that virtually no one knows about.
The National Archives of Spain alone have 350 million pages of documents going back to the 15th century, ranging from correspondence to testimony to charts and maps, but only 10% of it is digitized and a much smaller fraction is transcribed. Hopefully with how good LLMs are getting they can accelerate the transcription process and open up all of our historical documents as a huge historical LLM dataset.
When you're looking at e.g. the 19th century, a huge number are preserved somewhere in some library, but the vast majority don't seem to be digitized yet, given the tremendous amount of work.
Given how much higher-quality newspaper content tends to be compared to the average internet forum thread, there actually might be quite a decent amount of text. Obviously still nothing compared to the internet, but still vastly larger than just from published books. After all, print newspapers were essentially the internet of their day. Oh, and don't forget pamphlets in the 18th century.