While H 1610 provides guidance on constructing groups of fictitious characters in LCSH -- I'm curious if there's any instruction out there for the 'Imaginary' constructed subject headings.

Examples:

Lyra (Imaginary place)

Rama (Imaginary space vehicle)

Sweet Valley Middle School (Imaginary organization)

I already have asked and understand why they are in LCSH and not the NAF, this is not about that. 

I'm specifically asking if there's a reason or instructions as to why they're qualified as 'Imaginary' as opposed to 'Fictitious'

thanks!