Recoding was not carried out.
The categories do not represent highest attained level, but years in education.
The category "minimum years" (code 1) contains around 70 percent of the population.
This seems far to high, and is not comparable to the frequency distribution of the later German datasets.

If LIS users want to pursue a recode they may do so on their own responsability.
However, LIS questions its feasibility, and advices not to recode.