Album Logic - Sheetlets

I am only familiar with Mystic Albums - but I wonder what is the logic of including a sheetlet in the album pages or not. I'm not sure I see a pattern but some observations I have are:

1. Sheetlet is included if the 20 stamps are unique (e.g Legends of the West),

2. But, Legends of Hollywood stamps are not unique, but are included in the album,

3. But, Star Wars Yoda and Bob Hope are not unique stamps on sheet and they are NOT in the album as sheetlets, is that because they are not part of a series? -

4. But, the Disney Series looks like they should be in album as a full sheetlet, but they are not.

5. Of course some stamps like Greetings from America just don't fit an album page so they are separated.

So do other albums have these quirks?