Trust me, using United 1K 'Systemwide' fully confirmable in advance upgrade certificates, it happened on all UA flights. These was near always NC or NF inventory, and one could plan trips easily in advance to use it.
Flew SYD-USA-Latin America round trips around 30 times for starters. About 900,000 real BIS
miles. And to Europe near the same kind of number of times, via the USA. Similar miles there.
The NETT price coach tickets to South America or Europe generally were $A1,700 return. Often closer to $A1,000 RT on sales or promos. London was under $1000 for a while via the USA. The pure miles one earned, was worth near that when elite bonus added!
There were ZERO, repeat ZERO upselling of upgrades at gates or online. in those days.
*ONE* Systemwide let you fly SYD-LAX/SFO-IAD or MIA -and then to EZE/SCL/MVD/GIG/GRU/LHR/FRA/AMS/BRU/CDG, even Russia etc, upgraded in advance on all legs. 30 hours of flights per Cert. All 1Ks got at least 6 SWU Certs a year.
As long as no 'stopover' was more than 24 hours, all was good. Hit SFO, and the nearest hotel, have a relax for 23 hours, and onwards to next city. .
All UA USA domestic/Canada/Mexico flights were again full upgradable in advance using
'500 miler' certs that were more or less unlimited to elites and also full transferrable. 2000 miles transcons = 4 x '500 milers' etc.
Those were the days. Certs then were PAPER, fully transferrable - heavily traded on FT etc, and 'Bearer Bonds' essentially. UA agents often forgot to collect them. Partner agents NEVER collected them.
I'd start the flight in say MEL or ADL on Ansett. Who'd never heard of a SWU .. all they could see were confirmed upgraded flights, and would cheerfully issue boarding passes to Sydney and the USA. SWUs were meant to collected at
FIRST flight of an itinerary, otherwise no-one in UA had a clue.
Those were certainly the days.