Zugzug: I can't really comment on things that took place two decades ago since I wasn't a wizard then, but I can comment on things that has happened while I've been admin. Yes, there has been both players and wizards who cheated in different ways. That's not something we try to hide, but not something we usually announce either. I've caught quite a few players during my time as AoP, and I dealt with (I think) a total of three cheating wizards during my time as AoD. The wizards were, just like the players, punished for their cheats.
At the time I considered, and we discussed, if we should start naming cheaters in public, and there are pros and cons of doing that. Doing it could act as a deterrent for others, and it also helps to show players that cheaters (wizards included) don't get away with it, which definitely could be beneficial for mortal-wizard relations. On the other hand, publicly listing a wizard as a cheater would basically "kill" the career of that wizard, and publicly branding a player as a cheater would be a very hard punishment as well. So, is it worth that? Or is it better to handle it internally and give them a second chance (at least if the "crime" is relatively minor)? I opted for the second approach, since none of those I caught did something horribly bad. But if someone repeatedly cheats, or a wizard cheats so badly they are deleted, then I am not against publicly naming them to set an example. We've done so in some cases in the past, the most recent example being Irk. For minor incidents I think it's better to handle it more privately.
As for the quest experience:
Well, yes, I could look at a player and notice they have more QXP than the cap, and wonder how that happened. Unfortunately, there is usually no record on _how_ a player got their XP. Sure, you could check all their quest bits (the thing that saves which quests you have finished) manually, and compare it against the total quest XP they have, but that would be a very time consuming mess to untangle. And even so, I would have no idea how they got the "extra" QXP. If the character is very old, they most likely have XP from old closed quests (like in old Emerald), and they most likely have some amount of event reward QXP, + the weekly quest + possibly rewards for other things they have done. And they could also benefit from being created at a time when quests were more rewarding. But Genesis is 30 years old, and some players are 25+ years old. There are A LOT of ways they could have both gained, and like in Daerin's case, lost QXP during the years.
Our rules and policies have changed a lot during this time as well. For example you obviously don't get punished for using quest solutions these days, but once that was the case and people lost QXP as punishment. QXP was sometimes also used the other way, to reward players who did something exceptional for the game or community. (These days we tend to use imbuement stones as rewards instead) Unfortunately, there is usually no record of these things, and if there are, the amount of the reward / punishment usually isn't mentioned.
So, yes, some (very few) players are above the cap in terms of QXP, but it the majority of cases it's most likely due to being old or simply being lucky and creating the character at the right time in history. Could some have cheated? Yes, it's obviously a possibility. During 30 years, it's of course likely that some wizards and players have at some point cheated and gotten away with it. Did some cheats include QXP? No idea.
Now, I have looked into these things a couple of years ago (when I was AoP), and from what I learned we're talking about perhaps a handful of players who still are active, and they are all very old characters, and we're not talking about a lot of extra QXP either. So, my conclusion is that they got it mainly from old quests, events, and possibly some other reward, or was created during the time when you gained more from quests. I have definitely not found any players who has as much QXP as you claim. Not even close. But if you know of specific player who has as much as you claim, I am only a mail or PM away.
As for the QXP cap and the QXP multiplier thing, Gorboth's post from when the cap was introduced, and the discussion that followed is still around on the forums: viewtopic.php?f=27&t=1082
It's written 9 years ago though, and I some things have been adjusted and tweaked since then. For example the quest XP progress indicator was added, and the cap was also set somewhat higher than the combined amount of XP for all quests. So, Gorboth's statement saying "if you solved all quests in the orbs you have reached the cap" is for example no longer valid. So, don't see everything in that post and thread as facts today, but rather as a piece of history where you can read about the reasoning and discussions when the cap was originally introduced.
That's basically all I know about this. Hope it's helpful to clear out some rumours and misconceptions at least. See, Zugzug, not your standard "goto"-answer!