Alphabet soup, right? And if that weren't confusing enough, United's website cautions Singapore customers as follows: "Please note that the booking class shown on your ticket may differ from the booking class relevant for mileage accrual."
Even United seems a bit uncomfortable with Singapore's policy, noting, "The miles accrued are determined by the operating airline."
Assuming that you indeed flew on one of the ineligible fares, you have no recourse, legally speaking. There was clearly a miscommunication between your agent and the airline and you suffered the consequences.
I would suggest that you pressure the agent to petition Singapore to award the miles as a goodwill gesture. Because they serve as sales conduits for the airlines, travel agents have more clout than individual consumers and often can wrest concessions that would normally be denied.
The real problem, however, is Singapore's confusing, ambivalent policy and the carrier's proven inability effectively to communicate that policy to the traveling public.
As a matter of both marketing efficiency and simple fairness, the airline should either embrace a more inclusive mileage policy or find a way to communicate unequivocally which tickets are mileage-eligible and which are not.
That's what I told my boss at Singapore almost 30 years ago. It's no less true today.
Tim Winship is editor at large for SmarterTravel , as well as the editor and publisher of FrequentFlier.com, and a frequently quoted expert on frequent flier programs. SmarterTravel provides expert, unbiased information on timely travel deals, the best value destinations, and money-saving travel tips.