If you have run out of updates, you are out of luck.
Just tried to update my S3 Sportback, delivered in Australia in February 2014. The most recent update available from MyAudi for this car is 2016/17, with 2017 shown as available if I buy a new licence. One of my siblings has a S3 Sedan, delivered January 2016, so downloaded the 2017 update through his MyAudi account.
2017 Update via SD card worked fine in his car, but came up as "no update could be found" when attempted in mine. While both cars were eligible for updates, we could update both cars with the same downloaded update without any issues.
This suggests that the "5 updates after the version shipped" rule is applied in the car's system update software, not coded into the download.