To add my 2 cents as I have owned and re-shafted multiple sets of the 0211ST. They don't require the center caps. As I doubted myself for second, I just put a center cap on a .355 shaft and inserted into an 8 iron head that I still own of the 0211ST, then barely went in. Does not require the cap. Similar to the Sugar daddy wedges.
As for the PXG collared ferrules, I have no issues with creep. I will use a wire brush and rough up a small area on the bottom inside of the ferrule, a tiny dab of epoxy, push the ferrule up in place, then use your epoxy and go.
Good luck.