I can confirm that I have never seen these items appear in my games.
As far as I know - and I'd be happy to be incorrect here - Likelihood: N/A (That is, not defined) means they cannot be acquired randomly; they would have to drop from a specific creature or be a quest reward or something along those lines and I cannot find that information anywhere...
That is exactly what the likelihood tag does.
Also, to the best of my knowledge, ultrarare items (Ereog's Token, the Ring of Mastery...) don't drop randomly, even with a likelihood definition since no treasure yields that type of RarityDisplay.
I' really surprised that DLC03 items listed above are not dropping since they are supposed to be common and 390...
I'm afraid there is some hard code issue when it comes to common items. When I was updating my items mod Black Market Bazaar, it was my intention to add about 10 common items to the mix. After playing several games, not a single one showed up through random drops. Also for months now, I have added custom armors to my games which have a common RarityDisplay and a Likelihood of 400 and, likewise, they never appear randomly. They used to, a long while ago, but something happened along the way to... some patch?
Which brings us to the 4 missing Loot Pack Scrolls... Same issue?