In what appears to be a case of miscommunication, the FIA had not been informed that Pirelli usually accepts the earlier measurement – with the tyres fully heated in their still connected blankets – as its definitive official "starting pressure."
When Bauer did his extra checks, it was at a stage when Pirelli had already accepted the Mercedes tyres as "legal", while knowing that, with the blankets disconnected, the temperature and pressure could only drop.
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The Stewards also accepted that once the cars started moving, the tyres heated up again, and the pressures went up. Indeed, data from the cars showed that throughout the race the Mercedes tyres stayed well above the minimum requirement, and the FIA was satisfied by that.