I'd be highly suspect of that 10% number. I'll say it straight up, if they did in fact claim that number then it's either exaggerated or a manipulated statistic.
Like if the Raiders said 10% of their crowds are people from outside of "the Canberra area" but included Queanbeyan, Murrumbateman, Royalla, Yass, etc, in that 10%. It'd probably be technically true, and the statistic sounds impressive, but it's not really that impressive at all when you layout what the stat actually represents in real terms.
Not all memberships are equal either... The majority of memberships are simply glorified merch sales that are meaningless in the grand scheme of things.
With the exception of memberships that come with season tickets and/or entitle the owner to voting rights at the club, memberships are just tools to manipulate potential sponsors and partners into thinking that the club's support base is larger and significantly more lucrative than it actually is, or to push tickets at a highly reduced rate without it reflecting poorly on the club.
Frankly, if the industry wasn't actively trying to deceive people then non-ticketed, 5/3/1 game, interstate, toddler, free "memberships" given to juniors, etc, wouldn't count to membership numbers, and would be sold as their own thing. Not that that's a realistic chance of ever happening though...