<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by LAX 1K:
United's policy on upgrading has always been if you get a COMP before July you get it until March of the following year. If it is July or After... you get it for that year, the next year and expires March of the following year.</font>
No direct experience on when United's cut off date is, but some posts on the United forum suggest that it is October rather than July.
See for instance
http://www.flyertalk.com/forum/Forum50/HTML/020957.html