This is a re-release from 1986 of the original from 1980. I wrote about it in March 2022. So what more to say about it now? Well, having read a bit about his other masses, including the the other he created for the city of Mariazell in Austria, I can more clearly see the pattern. Also, I discovered there is a very ambitious writer of the Dutch wiki site, that offers considerably more information about these masses than the English version. A rare phenomenon.
It is unclear when exactly this mass was written. The autograph is from 1766, but parts of it are stylistically so different, they are more probably belonging to a period seven years later. More proof of that theory is found in the paper itself: these particular fragments were written on paper that was used during the period of 1769-1773. Reading about this I recognise the method of research from the time I studied medieval history.