Back in the 90's, Qualifying Blue (20 flights in your year) would earn 1 Upgrade certificate, Silver (50 flights) 2 & Gold (80 flights) another 2. These could not be used on international flights. (There were also distance criteria for status but I never really took much notice.)
After the turn of the century this changed and an "Upgrade Credit"s could be earned every 250 SC's, this was soon after changed to one every 450 SC's. For the first time since I joined, international flight could be upgraded.
One or more UC's could be used to upgrade a flight; the length/type of flight determined how many UC's were needed.
Initially an upgrade could be requested a certain number of days before departure, this changed to a varying level depending on one's status. ISTR something like 90 for Platinum, 60 for Gold, 30 for Silver - the exact detail escapes me at the moment.
After that it was changed so that simply U class for (eg) business needed to be available - no waitlist, if U was not available then no upgrade, although you could request later. This was for both domestic and international flights.
In 2005 this changed and UC's could no longer be earned, "loyalty bonus" (being points) were introduced and 5K could be earned every 450 SC's.
The SC's accumulated and required for your next "loyalty" bonus continued to accrue, regardless of membership year.
More recently, Qantas increased the earn to 8K, capped it a 4 per year and the SC accrual needed to be 500 on QF/Jetstar. At this time they also introduced the count reset at the end of a membership year.
Looking back, some years I did very well. My year that just finished was the first time since I joined QFF in 1994 that I did not earn a single Upgrade Certificate nor Upgrade Credit nor Loyalty bonus.
I did earn just over 1200 SC's, of which obviously less than 500 were earned on QF/Jetstar.
I guess I am no longer that loyal of a customer.