How do you distinguish fictionkin memories from fleshing out backstories that were left incomplete in the source material? I can’t tell if I’m having memories or if I’m speculating.

Its a tricky question, anon, and there’s definitely some grey space and room for questioning. Generally the way I tell a memory is if it seems ‘effortless’, like something that just popped into my head naturally. Another cue is definitely if the same memory/idea comes up again in more than one context, and if the memory makes sense in context with other memories you have.