Originally Posted by
joe_miami
I was one of only four people upgraded from J to F on a flight that went out with all 26 J seats and all six F seats filled, so wherever the ZL came from, it had to have happened afterward.
The Z* codes are UA's internal accounting mechanism for upgraded flights. Your P fare was likely an L-UP (underlying L fare basis, booking directly into business class). When you got CPU'ed, it put you into ON for boarding purposes, but ZL for earning purposes. It should have put you into ZP, but...
A call to the MileagePlus Service Center should get this straightened out.
(er, except for ZN, which is a separate award bucket, and not an upgraded N fare.
And, of course, Z by itself is a business class fare.