That is a good point... There could be a couple of ways to do it really. First, they could put three horses and riders in generic chain on a spru. And perhaps throw a few heads and shields to fit the Norman look if they fit on there. Then they could produce extra sprus with different head/weapon/shield options.
Either that, or they could do a sprew of six generic horses with tacking, and then separate sprus of riders, weapons, shields, and other kit (perhaps extra horse tacking) to facilitate pretty much any rider with an unbarded horse to ever have existed in the world! Sorta like the way GW does their mounted figs, with horses on one spru and riders on the other. That way, the same horses could be used for many different mounted packs. So, on four sprus they could provide twelve horses and twelve riders with lots of options!