I think you misunderstand the whole "4 years" thing.
When AO started in 2001, it was built by the original dev team with a 4 year story and timeline. The concept was that it's essentially be kind of a "Choose your own adventure" where the actions of the players in game would effect the storyline.
However, that idea didn't last long.
Around mid to late 2002 (I think) the original storyline developer left (was fired, I think) when FC decided to develop the "Shadowlands" expansion. At that point, the 4 year concept was dropped and work was made to keep AO a constantly sustainable MMORPG.
The problem is, that means the inital development of the game, and the actual result are two different things. So stuff like mission and corpse IDs, which were "shortcutted" by the original Development Team now have to be addressed as we are over twice the original intended lifespan of the game.
It's like you plan for a vacation, in which you add take a months worth of necessities, more than enough you think as you're only supposed to be there for two weeks. Only hey, look, civil war broke out in the country your in, the borders are closed, and you can't leave! Now it's been two months (almost three) and you're out of your necessities - you need to acquire more.
That's essentially the type of situation. Funcom never planned the game to run this long. The code is past twice it's lifespan and is showing it's age
I suspect we can expect to see a lot of these issues cropping up as the game gets even older.