I appreciate that but even when going through the stack in the proper order you still come up with a close approximation that may or not be reflected by an individual roll.
Though I would inquire at this point what the actual purpose of the lootprobabilitytemplate is then.
There are two versions of templates. Some depend on player loot level, some represent just a fixed percentage (the latter are the ones that have the short forms med, low, verylow...).
When they are used somewhere they usually are in a list with other items that either don't have a lootprobabilitytemplate or a different one. For example rareOres:
<lootgroup name="rareOres">
<item name="resourceSilverNugget" count="1,5"/>
<item name="resourceGoldNugget" count="1,4" loot_prob_template="medLow"/>
<item name="resourceRawDiamond" count="1,3" loot_prob_template="veryLow"/>
</lootgroup>
If you find a rareOre then the program looks at this table. A silvernugget is probability 1 (or 100% if you think about probabilties as percentages, the default), gold 0.35 and diamond 0.05. But these are not the real percentages because they would sum up to more than 1.
So the program sums up those probabilities: 1+.35+0.05 = 1.4 . Then it divides all probabilties by 1.4 so they sum up to 1 or 100% again. And then picks one line randomly according to those probabilities.
In this case silver would have a probability of 71%, gold a probability of 25% and diamond of 3.5% only.
Loot level dependant probabilites work the same, but the raw percentage value they have changes with the loot level. So they might have a very low probability with a low-level player and gain probability with time. In consequence other items in the same list lose some probability.