Okay, I found the part that you're talking about at <lootgroup name="groupJunk" count="all"> So we stop calculating after 1 cell giving us a probability of glue at 5% but if we're going to work out an average number of glues for a set of containers, we have to then figure stack size into it as well. Not sure where stack size is even represented here or how it's calculated, because from experience I know there is a great deal of variation in the end result. I suspect that since the end result of how many you actually receive is higher than the numbers I would guess to be the limit that something hokey is going on here.
The number of items you receive is based on the count in that subgroup, randomized equally based on the range.
In your example for glue, it is stated as
<item name="resourceGlue" count ="1,2"/>
So you have a 50/50 chance of getting 1 or 2.
As another example, cloth in the same group
<item name="resourceCloth" count ="1,5"/>
You should have a 20% chance of getting 1,2,3,4 or 5 pieces of cloth if that item was picked
But wait, there is more
<!-- cars-->
<lootcontainer id="19" name="cars" count="1,2" size="7,4" sound_open="UseActions/open_vehicle" sound_close="UseActions/close_vehicle" open_time="4" loot_quality_template="qualBaseTemplate">
<item group="groupCars"/>
</lootcontainer>
As you can see, the cars container has a count of "1,2" which means you did have a 50% chance of going through the groupCars twice. That means, if you are lucky, you could get potentially 2 picks of glue meaning your potential glue haul could be 2-4.
There is a mod out there that will generate the percentage chances of loot drops as you play the game
https://www.nexusmods.com/7daystodie/mods/2067
This is from a gamer that goes by
@Boidster Boidster seems legit....but it seem like the mod was being pushed pretty hard at the beginning so you might want to be weary of them. Seems awfully helpful which always indicates something is up