I agree there is a huge difference between CM Larb and Isaan larb. My other half is from Fang and makes/eats the CM version with liberal use of offal (mainly liver), garlic, black peppercorns (which I assume is the Makwen) and fresh pigs blood. I much prefer the Isaan style made with minced pork and no offal added for my own personal taste.
I was served it in Isaan once at a family gathering where it was made with raw beef and blood - no cooking whatsoever. I tried it out of politeness and made all the correct noises but can't say that I enjoyed it or would like to try it again.