The Data Plumbing Illusion

Senior Data Engineer interview at Anthropic, and the interviewer asks:

“You swapped Common Crawl’s WET files for your own extraction off the raw WARC files. Same URL list, same filters, same model, but your benchmark scores moved. Your teammate says extraction is just plumbing. What do you tell him?”

Don’t say: “The extractor must have a bug, I’d diff the outputs.”