What is a no-drawback rule?
Duty drawback is getting back the duty you paid on imported materials once the finished product is exported. Some agreements limit it, so you can't have both the refund and the lower rate in the partner country.
Why the limit exists
Without it, a producer could bring materials in duty free through drawback and then sell the product into the partner market at the preferential rate. The agreement sees that as getting the benefit twice.