Late post, I know, but old forums can learn new tricks. Forums, dogs, cats, whatever. This is why I don't make jokes as much anymore. Um, anyway, back on track.
One of my current playthroughs I am doing rn was my SoulSilver 100% run. Switching between three of those runs and Shiny hunts led me to weird instances where I didn't play some games for a month or more. Anyway, I had found a Shiny Ekans on Route 32 shortly after beating Falkner and getting all of my Route 32 encounters. I was pretty excited and kept what is now a beautiful Arbok on my team up until around National Park. Fast forward to after getting access to Surf. One of my mandatory backtracking routes took me to the back room of Dark Cave, as I stull needed Golbat, Graveler, and Wobbuffet. After failing one Wobbuffet and going through embarrassing save data mistakes, I caught Wobbuffet and was looking for items in the room via the Dowsing Machine when out of nowhere, a Shiny Zubat flies onto the screen. I caught it after being struck speechless for an entire minute, and upon further inspection, I noticed that not only it had a Jolly Nature, but it was the exact same level as Arbok was when I had placed it back in the PC! These encounters followed a five year long drought of Shiny Poison-types, and got me to believe in the odds of potentially finding as many as four full-odds Poison Shinies, counting my Foongus hunt in White I've been working on, all within the same level range and in the same calendar year.
JUST LET THAT SINK IN.