In my experience also working for a very large corporation managing a large multi-national team, when you're forced to down-rate someone for bureaucratic reasons, the most common method used to offset the insult is to provide a larger than standard equity grant or annual bonus. For example, if you are only allowed to give "Exceeds" to one of two deserving individuals at the same level, perhaps the one being set up for promotion only get the standard bonus but the other one gets an extra 50% of their anticipated bonus. None of this is fair, but it's an example of how managers try to be reasonable without violating company policies.

Almost all managers would spend more on labor than they're allowed, and also believe their employer's comp policies are at least somewhat "broken".