Not sure if this adds anything (I didn't see YC77 listed before):

YC77 is an RT Saver Award in Y from Mainland U.S. to North Asia, booked in May 2014 for 70,000 miles. For my specific routing to ICN: RWD YC77/NONEND/-TRAN;VALID UA/OZ;NOT VALID AFTER 5/7/2015

Also, in March 2014, at least ZC20 (tested on RT in Y within Mainland U.S.) and ZC53 (tested on RT in Y from Mainland U.S. to Europe on partner airline) were Standard Award equivalents of YC20C and YC53.