Neganova and Daedelus are correct but they're purposefully avoiding the meaningful and true mathematics provided by voidspark. If someone's goal is to get the mount one time. The number of attempts they make do indeed increase the chance of having that one time occur. The chance for each individual attempt is unchanged unless Blizz is doing something fishy on their end like with the coin rolls. However, the chance that "NONE of 458 attempts will produce a mount drop at a 0.79% drop rate is indeed less than 1%"
What does this mean for the OP (and any other interested parties)? That if 100 people collectively made 458 attempts each. Statistically 99 of them would have found the mount, and 1 would still be looking for it. Each and every one of their 45,800 attempts would have had the same 0.78% chance, and while we're in the realm of mathematics, the mount would have dropped 357 times meaning that a few of those 100 people got it twice (or more!) the lucky dogs.