I appears that I was wrong in my previous post.
I have killed even more bosses.
I have listed 3x3 items but there are a lot more.
When you start the EB at level 1 the above 3x3 items are not even visible.
There are 6 “tiers” each having a set of 3 items.
When you start the EB at level 1 you see tier 1 as common, tier 2 as uncommon, and tier 3 as rare.
After killing some bosses it shifts one tier up:
Tier 2 becomes common, tier 3 becomes uncommon, and a new set of 3 items “tier 4” displays as rare.
Tier 1 is gone.
The same happens killing some more bosses.
The last shift is around boss 102 when the final tier 6 (with the refill and the mods) jumps in as rare.
I took better note this weekend. See my next post here.