The core of the maneuvers taught in Underwood's Combato and Fairbairn's Get Tough are still present in most western combatives systems today. The polcie combatives courses I've taken all hae strong elements from these systems in them. I would say that Comabto/Defendo/Defendu is a suite of styles that were born at roughly teh same time in a few different places, which have since melded and grown into the various present-day North American and British military and police CQC systems.
I learnt some of it as; All In Fighting or Gutter Fighting, though I'm finding mixed resources online concerning if it is the same thing/different name so I'm a little confused.
I'm referring to the Fairbairn-Sykes methods.
Some of these I learnt from my Grandad, others from the books of which I have two.
As a side line, if anyone wants a laugh try and get hold of a copy of; Silent Killing - Nazi counters to Fairbairn-Sykes Techniques. It is quite literally the most pointless thing I've ever seen.
I wonder how/why these Nazi methods were created but I knew better than that in combat before I ever even began training...age 6.