go back?
Short answer: Yes, in the sense that a fictive is formed in a system and that a person who is fictionkin realizes the fictomere later on in their own life. But other than that, there's no widely accepted differences.
Long answer: It depends. For us personally, there is a pretty big difference between the feeling of being a fictive towards a source vs being fictionkin. Neither is more "real" or "fake" by the way---there's an old narrative that fictives are more "real" than fictionkin which is not true at all. In our personal collective experience, our system's fictives feel like their fictive identities are their kind of "home base". There wasn't really something BEFORE that, if that makes sense. Peridot (HI I'M WRITING THIS) didn't have an identity before Peridot, he just came out that way. Meanwhile, when our fictives gain fictionkin identities, it feels like layers on top. Like unrealized aspects of ourselves to supplement to our senses of selves. To be fair, we don't take fictionkinity as "seriously" as most due to past trauma (it's a long story) but our fictionkin identities are still very important. For example, Peridot and Acht are very close in a brotherly way not due to their fictive identites but due to their fictionkin identities' influence (Five Pebbles and Looks to The Moon). We're sure that for some systems, there is absolutely no difference in the feeling of being a fictive VS being a fictive with fictionkin on top, but for us it's an important aspect of how we function and live our lives!
Sometimes the lines between a fictive and a fictionkin identity can get a bit blurry though. When Peridot (HI I'M WRITING THIS) first formed, very shortly after he first started speaking, he requested to watch Gravity Falls. So very early in its development it acquired a fictionkintype from Gravity Falls and for a long time identified very closely that way (NOT THAT I DON'T ANYMORE, JUST NOT AS INTENSE...). So he considers that "fictionkintype" kind of half fictive-y in its "identity feel" because of how intertwined it was with his initial development. Wow, aren't brains so interesting?