The NAT0030 and NAT0030A files are produced in the batch based on enrolment in the batch.  Different data has different rules. 

NAT0030

If all the qualification, course or skill set associated with enrolment activity are listed on TGA, then you need the NAT0030 file is required. Please see NCVER’s information here: https://www.ncver.edu.au/rto-hub/data-validation/avetmiss-8-nat-files

NAT0030a

That NAT0030a is required if the qualification, course or skill set associated with enrolment activity are not listed on Training.gov.au (e.g. SG codes). This usually happens when a code is created for a state specific purpose, like when Smart & Skilled creates SG codes for their skills groups.