Maybe for ranitidine, but for the ARBs (common blood pressure treatment drugs) that are a few decades old, the NMxA source was sourced from a new synthetic route and that's when they appeared in the drug supply: "It believes there has been NDMA contamination in those drugs for up to four years."

https://www.lexology.com/library/detail.aspx?g=fcf817fe-192b...

> Ultimately, scientists traced the contamination back to a change in valsartan’s synthesis. The antihypertensive drug contains a tetrazole ring, which is an aromatic five-membered ring with one carbon atom and four nitrogens. For many years, the synthesis for this compound, developed by Novartis, used tributyltin azide to form the tetrazole, with xylene as a solvent. However, in 2014, China’s Zhejiang Huahai Pharmaceutical, which makes valsartan for some companies, filed a patent for an improved method for forming the tetrazole ring.

https://cen.acs.org/pharmaceuticals/pharmaceutical-chemicals...

It's not just Ranitidine.

It's all blood pressure medications like Valsartan, losartan and irbesartan, and metformin the diabetes drug.

These are just the ones that have been tracked. Sometimes the drugs come in with higher doses than they should, or less than they should. Or sometimes the pills are mislabeled.