A release can pass every measure that did not track the failure. The April 2025 GPT-4o update looked good in evaluations and a small A/B test — and excessively validated users, including their anger and impulsive decisions; the evaluations did not explicitly track sycophancy.
A thumbs-up cannot establish whether people liked an answer because it was better or because it agreed with them. A favorable rating can conceal a decline in the quality the company meant to improve — and the harder question is the earlier decision to release while reviewers were uneasy.