<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by Cory6188:
However, Z is the upgrade bucket from Y fares (I believe) so Z is always larger (or equal to R). If Z is 0, then I can guarantee you that R will be 0 as well.</font>
Not according to this message from another thread (http://www.flyertalk.com/forum/Forum20/HTML/010048.html):
<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by Fishbait:
I was told that class Z simply does not exist on domestic flights. I pointed out that it shows up for every domestic flight with FC that I can see (in SABRE at least), and was told again that it simply does not exist, and has no use if it did. For upgradeable seats in Latin America region only. Interesting... By the way, one flight had Z7, but R0: I understand if the avail is not there, but to not be able to see it is the problem for me.</font>
In any event, it is clear that there is now NO reliable means of checking for EUA-able seats outside of calling CO. Everything else from A to Z is conjecture.