In the case of PerksPlus the account administrator adds the MP# of all employees to the PerksPlus account [there's also a "Tour Code" that uniquely identifies us if we were to use a TA tot ticket, but we don't]. UA uses that to correlate our corporate travel spend at the end of each month.

IIRC, for large corporate accounts with negotiated fares the company is required to nominate (a) TA(s) to issue any tickets based on those private fares, so UA can track what travelers are flying on those private fares.

That said I don't believe that UA is blocking travelers from a specific company from achieving GS, but rather I sensed frustration that those who aren't "working for it" are being given it on a sliver platter while those warrioring on the road have to work for it...