Nick/Johannes,
Not sure if this helps or hinders but there was an article by someone called Julius R Gaal from the December 1965 issue of Flying Review International discussing whether Luftwaffe aircrew's claims were valid or inflated!
The article
"The Luftwaffe's Kills" contains reference to the points system.
The points system is mentioned in para 4 of the section entitled "What are these figures worth". It does not go into great detail as this was not the main thrust of the article.
As usual with articles of this vintage very little in the form of references exist.