There are different lists -- such as the true upgrade waitlist which only the agents can see. No sure there is a list of successful upgraders the agents can see or not.

What is it passengers can see?
On mobile devices or on united.com, the standby upgrade list (but most refer to it as the upgrade waitlist -- but it is a different list than agent's list).
This publicly visible list will show some of those upgraded for various reasons but not all (or all the time). It does show the upgrade waitlist order of those that have checked in. This is NOT the true CPU (or miles/GPU/RPU waitlist) but rather it is the Gate upgrade standby (/waitlist). The gate list is prioritized slightly differently (not entirely clear how -- may be related to YBM folks and use of check-in time as a tie breaker -- but never has been clearly stated), only shows the waitlisted folks that have checked-in and may show some that have been upgraded even if they have not checked-in.

In particular to the OP, on international flights, those that clear at booking or long before the flight tend not to show as clear on the publicly visible list.