- and from 2019 adjust the maximal value by the average worldwide upstream bandwidth growth. That's about 10-20% per year - this estimation being based on this document (already a little bit old, but should not have changed that much) which suggests a 10% yearly increase between 1980 and 2010 and then a slightly accelerating rate.
Well, that's the lowest estimate of internet bandwidth growth I've seen.
Another data point would be Nielsen's Law: "Users' bandwidth grows by 50% per year (10% less than Moore's Law for computer speed). The new law fits data from 1983 to 2016." https://www.nngroup.com/articles/law-of-bandwidth/
Or this academic paper, which looks at separate segments, and notes that growth has fallen from a 20th century 'mere doubling of rate per year' to 20%-30% in industrialized countries, and 65% cellular bandwidth growth worldwide. http://www.dtc.umn.edu/~odlyzko/doc/webtraffic.pdf