Every plant has one. The senior process engineer who knows the right ramp rate for the new alloy run, the cycle-time trade-off the OEM signed off on three years ago, the sequence that gets a mixed-model line back to nominal in twenty minutes instead of an hour. When they're on rotation, the line runs well. When they're not, it doesn't.
The 'official' SOPs are PDFs in a shared drive, last touched in 2017. The actual playbook is a Slack thread, a few whiteboard photos, and a Wonderware screen-capture nobody has time to formalize. Onboarding a new engineer means re-learning what was already learned.
Parameter tuning is done by feel. Nobody can tell you, after a good shift, whether the same parameters would have worked yesterday or last week. The plant produces good runs and bad runs, and the difference is treated as luck because there's no instrument to compare them.