It appears that Semic used the same ISBN for both the first and second print of books. So, for example, both the first and second print of #3, Don Martin vaers go, have the same IBSN, even though they must have different publications dates (not listed in the book).
Usually, the ISBN increases with each new book. So, #3 ends in -3838 and #4 ends in -3854. It appears that #2, Leve MAD, has an ISBN of -3870. That would put the number later than both #3 and #4.
The initial ISBN identification format was devised in 1967, based upon the 9-digit Standard Book Numbering (SBN) created in 1966. The 10-digit ISBN format was developed by the International Organization for Standardization (ISO) and was published in 1970 as international standard ISO 2108 (the 9-digit SBN code can be converted to a 10-digit ISBN by prefixing it with a zero digit '0'). That explains the missing leading zero(s) in some of the German books.
The publisher part of the last Danish book changes from 4560 to 7708. We don't know why.