No, just a statement of fact
I think you've hit a really valid point: Clube and Napier played fast and loose with recent chronologies in
their books, and thus compromised their argument over injection mechanisms, which operate on much longer scales (millions of years). It appears they were focusing on comets at the start, while the Alvarez's, Morrison, Shoemaker, were focusing on asteroids.
What I've found is that in most of the softer fields (anthropology, economics, psychology, history, etc.) progress is flawed.
Whether this is a result of difficulty, or the nature of the fields, or other factors, I don't know.