The encounter slots are actually mapped thanks to the awesome people who worked on PIDRNG :0 Thanks to the program I knew my spread had an encounter slot value of 9, which in Lostlorn forest lands on Swadloon - that's how I was able to bring a Jolly sync with me. I originally planned to get shiny Cottonee, but looks like that will have to wait. ;-;
Nonetheless, I didn't believe mine was the first retail cart shiny anyway, though perhaps maybe it's the first retail shiny RNGed from scratch (rather than RNGed like the shiny starters, which is most certainly a fantastic accomplishment itself) that was also offered for trade on a trade thread, haha. I'm pretty sure most of the researchers themselves have plenty of their own wild RNGsand got them wayyy earlier than I did, but most of them don't really trade xD
But nonetheless, thanks for clarifying :) Once I get a copy of White I totally want to RNG my TID/SID somehow too *__*