It’s never officially been clarified, it’s like a lot of the speedway regulations very ambiguous and subject to interpretation. This should be shown in the GSA especially the final one, so it’s clear who get the discount, it clearly doesn’t just qualify if you rode NL or the equivalent in the past, it also depends on your nationality.
For example BWD rode in the NL in the past but didn’t get the discount because he rides under NZ registration in FIM events even though he holds a British passport.