Establishing LOQ at 30% is reasonably good and acceptable. If the values are consistently less than LOQ in all process validation batches and respective stability samples(ACC and LT), it is acceptable for skip lot testing. Moreover, it is important that there should be no sign of increasing trend in stability samples over the LOQ. Otherwise, you should bring in to routine testing.
Further, if the results are not detected you can omit the testing , but careful risk assessment and testing should be done appropriately as and when the process/materials are changed.
NDSRIs impurities are generating due to interaction of APIs with residual nitrate and nitrites from excipients, water, packing materials etc. In most of DP’s impurities are increasing during stability studies, different from classical nitrosamines. Risk assessment samples should be representative product shelf.