I noticed that some sources have different stuff from each other. For example, the essentials kit bundle has only dragon of Icespire peak and the digital one has all four adventures. Furthermore, that physical copy has an extra subclass for bard, cleric, fighter, rogue, and wizard classes. It also has a few extra  background options to choose from. I also noticed that some Pre generated character sheets have classes and species/races  and background options that are not part of the content from what I have available to me. And although certain adventures have certain monsters in the adventure, it is not a stat block on my list of content, and only accessible using the book in question like the tortle package and that ocean based adventure focused sea exploration and deep sea mysteries. Why is that? 

I think the relevant descriptor is bundle, the physical game in the box, can be brought digitally either alone or in a bundle, it can also be bought through Wizards as a digital/physical bundle. But the physical game 8n the box is not a "bundle" in the same sense as the other are bundles.