I remember first reading about Henry Lucas in the early 90s. Also watching the film Henry: Portrait of a Serial Killer (which is obviously not accurate, but a good film overall if you enjoy gore and violence 80s style)
I recall so many serial killer books mentioning how he killed over 500. So it is interesting now to see how those confessions came to be with the recent Netflix documentary.
However, because Lucas and O'Toole were drifters and constantly on the road, I do think they were capable and able to commit at the very least 20 murders. Hopefully DNA evidence will find more victims that may be out there.
Their tendency for extreme violence and perversion, along with John Walsh confirming that he believe Otis O'Toole murdered his son Adam (Decapitation) seems to me to be a obvious precursor for more violence and victims.