Actually, I misrepresented that a bit, the reality would be:
Attack result - target 1's DB = initial result.
Initial result maxes at 150 on target 1.
Initial result - 150 - target 2's db = second result
etc, etc. . . so the 500 example I gave above would only apply to 4 targets with zero missile DB.
In use, I find that wrapping the table on missile results most often happens with nastier foes than the kobold throwing a spear, and that almost all of the time it ends up being a hits result. (usually it's an open ended result giving say a 200ish total attack making for a 30-50 attack result on target 2)
thus, most of the time it's "The javelin thrown by the kobold strikes jerry in the neck, continues, and caroms off of joes shield with a clatter."
also, often there is no target 2, if nobody is standing behind the target, the missile or bolt goes on, perhaps striking an object like the wall. (I don't do JFK like magic bullets)
As to the unrealism of passing through the torso of a plate mail wearing foe to hit next target the results need to be tweaked to fit something realistic. . . .much like said kobold attacking said platemail wearing foe with a dagger in melee getting a slash result like "Blow cuts through foes shoulder and out the ribs, severing arm" needs to be changed. The crit text is just flavor and often needs adjusting. . .
So in a for instance where kobold bowman does a double open ended on two AT 20 wearing warriors that gets past their DB to to two E puncture results with high crit rolls, getting a "deep puncture into chest strikes major blood vessel, bleed 12/round, stunned 5 rounds" and "Strike to foes chest punctures heart, killing him instantly" I'd then ponder a moment and say to my players:
"The kobold releases the wooden arrow from his crappy makeshift bow, the wobbling arrow catches Jim just under the chin of his helmet, passing through a small portion of his neck that unfortunately includes both the jugular and carotid, continues on with most of it's force spent, and through utter happenstance strikes perfectly into the slit of joe's visor. It retains just enough force to puncture Joe's eye and lodge in his brain, killing him instantly. Jim, you're bleeding 12/round and stunned 5 rounds."