Empire of the Petal Throne refactored experience points table

In rule 600, it is clear that the basic experience system is based on OD&D. You get one experience point for each Kaitar obtained, with an exclusion for winnings from betting in the Hirlakte arenas, an obvious patch for some player that tried it. And 50 points for each HD of each slain hostile being.

Kill XPs only go to the last one to hit the target, explicitly not to the one doing the most damage.  It's curious as this leads to infighting regarding kill stealing and the like. It's probably not a big deal, since kill rewards are likely to be swamped by treasure XPs even at the 50/HD rate.

Treasure sharing is also discussed in rule 600 on experience points, perhaps because treasure is the main source of XPs.

Rule 630 gives a classic, D&D like upscaling by doubling XP progression table. There are two oddities. One is that after doing the doubling progression all the way up to level 9 (with a bit of flattening to reach levels VIII and IX, oddly only for Magic Users, given the D&D antecedents where they were deemed to need the most per level), the table does not just flatten out to needing the same for each subsequent level, it drops precipitously to a flat 10,000 for each subsequent level (though affected by rule 620). That is a huge drop, even accounting for rule 620.

Rule 620 appears to be a variant on D&D's rule about high level characters fighting low level foes having their experience points reduced for it. But instead it applies more simply to all experience points gained at the level, so the characters get a double whammy going up to level IX, both a doubling of the amount needed and a scaling divisor that makes it even harder. A campaign played straight up is going to have to pour gold through the PCs' hands to keep them levelling up to IX. Since it is a flat effect, there is really no good reason to bolt rule 620 onto the table in 630, other than to make 630 look more like D&D. You have two rules doing the same thing, the intrinsic doubling and then the experience point reduction patch.

It all says to me that MAR Barker was not a systems guy. I'm wondering if the rule about levels X and higher being so much easier than IX is intended or a bug. If it is intended, why?

Here is the refactored combination of rules 620 and 630, run up for a few more levels, following the algorithm specified.
I am rounding away the awkward 1's at the beginning of each level, for simplicity. Add them back, with the appropriate multipliers to account for 620 if you care.

Level	Total XPS Needed	New XPs needed to reach next level
I	0	2,000
II	2,000	2,000
III	4,000	4,000
IV	8,000	16,000
V	24,000	32,000
VI	56,000	128,000
VII	184,000	224,000 (184,000 for MUs)
VIII	408,000 (368,000 for MUs)	1,200,000 (900,000 for MUs)
IX	1,608,000(1,268,000 for MUs)	100,000
X	1,708,000 (1,368,000 for MUs)	200,000
XI	1,908,000 (1,568,000 for MUs)	200,000
XII	2,108,000 (1,768,000 for MUs)	200,000

So level X is the easiest level to get since level VI. But then it bounces back up and XI, XII, etc take almost as many each as VIII. Overall it strikes me as the sort of hodgepodge you get when layering systems without thinking about it too hard, instead of actually designing software or game rules. The trailing comment about how the seeming impossibility of getting enough to go from X to XI, is another hint, when VII to VIII and VIII to IX are the really hard levels, since you have fewer assets and tougher goals. Trying to come up with a rationalization, maybe the trudge to level IX represents your character getting into the upper reaches of society/administration, but once in, your path becomes easier to accrue more power?