Somebody mentioned this on here a few weeks ago, and it raised a bit of debate, but there was no proof offered that Barber actually does have a shareholding. Actually, I think the dullard (or @Bozza?) mentioned that in the most recent shareholders filing there was no indication that he had...
The one thing it definitely ISN'T is sell-on %ages, as they are so nebulous that there is absolutely no way to put a figure on them.
It will be add-ons, ie if player X makes Y appearances, or scores Z goals, or wins a certain number of caps etc, or potentially if the club achieves certain...