Unless you fail your PC, in which case you would do the stuff you failed.
How many people do you think actually FAIL a PC outright? As a former STC I can tell you the answer is bugger all. Sure there are some who might have a hiccup on the day and score a 1 for a particular section of a PC. Those that do should get some remedial training from the checker during the session, before repeating that section of the PC during the same session. It is quite rare for someone to fail a second time.
Funnily enough, most people can actually do the job quite well.
A large part of the RT session is currently wasted practicing stuff that most people don't actually need to practice to pass the PC. The whole idea of putting the PC first is to get it out of the way and then use the RT to do something that might actually provide more benefit.