Back at one of the CO dos, one of the executives shared that they definitely keep track of profitability for each customer. At the time, OnePass tiers were based on miles flown, and now we have a revenue-based model. But internally, they have calculated profitability. If they had this data 15 years ago, it can only be even more sophisticated these days. It would not surprise me if GS invitations were based on calculated profitability. There may be rules of thumb that say you need to be at or above $X dollars to get GS, but that might really be a proxy for what the average passenger realistically needs to spend in order for profitability to be above the GS threshold. This would explain why a) they don't publish a particular PQP threshold, and b) why there's a variance in peoples' experiences that nobody can quite put their finger on.