Indeed there were some stories of crews having FE's join them at a HCU who unbelievably had never flown before!
Also as an ‘aside’ to the main topic (so as not to ‘offend’ frodo_monkey!!) I don’t believe it’s that uncommon for some of the rear crew chaps to have little airborne experience prior to their OCU even in more recent times. Certainly the ab initio ALMs on my first cse joined us without their brevets and with only a handful of flights under their belts, they were presented with them on successful completion of the course. FEs used to do much of their training on an old Nimrod AEW ac at Finningley which could be taxied but not flown.
I’m not an expert on rear crew training but I don’t think they do a great deal of flying on their basic cse today, perhaps a couple of trips as a PA on the Phenom?