items-base-phb vs. items-phb

[ebullient]

I'm trying to create a custom compendium that has items only from a selection of sources, but I'm confused about items-base-phb, because it is in the PHB sources, but contains items from other sources.. and some of the items in that file, aren't in items-phb.

Is there a reason non-PHB items are in that file? Seems to run counter to the overall grouping of content..