Jabba had this problem from memory with his IFR Retard-Vehicle 10 and ended up doing his IFR is some beaten up old Piper.
What was the go Jabba?
I think perhaps it is because the Retard is in the experimental category.
Just for instance, looking at
The RAC Rates page, it says down the bottom "Instructor hire (own aircraft). Would that not mean that the aircraft does not have to be on the AOC?
Pyro