BriH touched on this with his high level adventures but a very high level spell caster is highly likely to have every open and closed list and every base list to the max. Obviously the rules in play can affect that. I am playing my lay healer in a game where almost everyone in the world has at least some kind of magic and every family has a spell caster.
In that game 10 ranks in learning a spell list is enough for automatic success and you can learn lists in parallel. You can learn one list for every powerpoint/level you gain. The GM also allows you to add your stat bonus to the spell gain roll if the chance is not automatic.