It may be possible to generate graphs back to 2013 or so using the same methods as today. I could also look in the database to try to get a good measure of saves over time. The longer you go back the less accurate the data may be, as not all metadata and dates are preserved (deleted save data is lost forever, for example).

From experience, I can tell you that the peak activity of TPT was in 2011 and 2012. This is when I joined and things were much more hectic, with a significantly larger community and much faster paced development.