I do not know of any particular reference that will explain it, but I will explain what I understand:
An anonymous block is not named, at least not in the classical sense. It is numbered in the block table and that is pretty much it. So for what that gets you, you cannot insert a block reference using the insert command. You can however, entmake one. Whenever you create an anonymous block, it is guaranteed to have a unique name (they are incremented numerically in the block table *U1, *U2, *U3 etc.)
When you have a block that is named with a random name as you have shown in your example, a block reference may be inserted using the insert command, I suppose you could also entmake the reference is you wanted.
The name as you have shown is a name just like any other named block. There is nothing materially different except the name is probably meaningless. It can be inserted and manipulated just like any block reference because it IS just a regular block reference, only with a weird name.
The added benefit of anonymous blocks is that if you create a single anonymous block in two drawings, both indexed at 1 (i.e. *U1) and you insert both base drawings into a third drawing, the anonymous blocks remain unique. On the other hand, if you create a block in one drawing named A$C0E547C8C and you create a block in another drawing named A$C0E547C8C with different geometry, then try to insert both of those base drawings into a new third drawing, the block named A$C0E547C8C will be redefined such that both instances in the third drawing will have identical geometry.
In essence so far as AutoCAD is concerned, *U1 does not equal *U1 if they come from different drawings, but A$C0E547C8C does equal A$C0E547C8C when from different drawings IF you try to put them both in the same drawing.
I hope this makes sense.