Those appear to be the actual numbers. Also, it did say
> There is thus a 50% chance of encountering a Shiny Pokémon in the first (roughly) 130 chained encounters.
"Roughly" means that the 50% mark lies around that point, mathematically. It could be anywhere as low as 120, or as high as 160. The fact that you still haven't found a Shiny is just a roll of the dice – no matter how favourable your odds are, there is still a chance of failure. Just keep chaining, and you'll get that Shiny. I commend you on having the patience to chain 200+ Pokémon, I was chaining fora Bold HA Tangela and only found two in 60, and neither was Bold. So I gave up and decided to breed for it.