Yes, UA ticket indeed and SQ tried to refuse to issue the boarding passes. I'm well aware about online/phone bookings on SQ stock but this was UA 016 stock ticket.

What I meant to say above - my card was copied somewhere, cancelled and I got a new one. Only the last 4 digits changed. I would have obviously taken the cancelled card with me but nobody has ever demanded to see anything on a ticket issued by a different carrier/travel agent.

Suddenly at the gate it was no longer an issue thankfully.