Had another look and it's a safe bet that the first digit of a Batavus road bike from the late sixties onward is the last digit of the build year. So that would make yours a 1978.

Here is what the I believe to be a 1977 example. The 1st gen. 600 supports that. 600 EX would be '78 or later.

The problem is that many people have apparently used the "sticky note catalog pages" to date their Batavi, so lots of false confirmations available.