Originally Posted by
motytrah
I'm a bit surprised DL wasn't matching CO on an I fare. Though CO will honor J cabin during IRROPs where DL will be glad to seat in you coach and pocket your cash.
While I completely agree with the OP about the M fares, I have had a different experience than you with Delta honoring business class. The other day, due to IRROPS I missed my flight from NRT to TPE which was booked in M and upgraded with a SWU. Delta immediately put me on the first flight the next morning on JAL confirmed in Business. But don't get me started on the trouble that M fare stirred up with my company...