You're not 62.53% guaranteed to get a shiny after ~26.5k encounters, nor are you 99.999% guaranteed to get a shiny after 300k encounters, as every encounter is an independent roll and doesn't affect the next one. If you do 300k encounters, it's just rolling a 1/27,000 dice 300000 times, assuming you're running donator. I get what you're trying to say, but 1/30000 chance will always be inconsistent over time.