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|
|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|