First of all, it depends on time of day and how many Elites flying.
Second, don't trust the maps, look at CO farebuckets on CO flights until after merger to help get a better idea of available UG seats.
Third, CO goes by fare purchased first + other reasons people would be on the waiting list you did not see.

The waiting list only shows up at checkin 24 hours before, as persons begin to checkin. The confirmed UG list will also appear at this time. The waiting list changes as people checkin and as persons may be upgraded. (They may have been holding back upgrades until 24 hours.)

Fourth, Presidential Platinums, GS, and CO Platinums go before UA 1Ks until new Mileage Plus program kicks in sometime in March. (Hopefully on March 3 as announced and there are no delays.)
Position on waitlist after 24 hours considers checkin time in some cases as a tiebreaker for some persons to get UG.

There are several other posts about Upgrades in this forum and specifically in the CO Forum you can read to more familiarize yourself with how things work. It is worth your study. Also, go to continental.com to read their upgrade rules.

The main thing to remember, is when flying on Continental before the new MileagePlus program starts, their rules prevail and you should use your OnePass number. When on UA flights before the new
MP program starts, use your MileagePlus number. After March 3, you will have a new MP number. If you don't have a One Pass number, you should status match and get one.
Good luck in the future. You only have to use CO rules on CO flights until the new MileagePlus program rules kick in soon.