United's leniency is more likely to manifest itself for higher-tier near misses. Still, that's no reason not to call and ask even if you're only shooting for Silver. Maybe even call twice or thrice.
One call is plenty -- among other things, MPSC agents do a much better job than reservations agents in documenting conversation history.
Like most airline-related things, the key is to never accept a "No" from someone not authorized to give a "Yes" in the first place. Front-line MPSC agents cannot upgrade accounts unless they fall into a narrow pre-determined band of qualification exceptions we won't know publicly, and cannot do anything on Premier 1K status upgrades. True power rests with the MPSC supervisors, who are authorized to consider and approve status upgrades (extensions) up to and including the Premier 1K level based on still-unknown but more flexible criteria.